The screen of an e-reader isn't like a computer or smartphone; it uses what's called electronic paper technology to show black print on a gray background. You don't get color on an electronic paper screen -- yet. The advantage to this technology is that it's very easy to read, even in broad daylight. Because it isn't backlit like a computer screen, it's also easy on the eyes, and a single battery charge will last for days.

How do you load books onto it? There are two ways. Some e-readers, including the Kindle and the larger format Sony Daily Edition, have a wireless hookup, so you can buy and download books from anywhere without a computer. Other e-readers require you to connect to a computer to download books via the Internet, which is much less convenient. Most e-readers have the capacity to store thousands of books, as well as music and audio books.

Where do you get these books? Each of the major vendors wants you to buy the books, magazines and newspapers from it, in its own special format that will thwart digital pirates. It's not a coincidence that this sounds like Apple's iTunes strategy. But you can download classic books free from Project Gutenberg, and some libraries offer digital loans through third-party companies such as Overdrive in formats these e-readers can display.

What else can an e-reader do? Most will store and play music and audio books like an MP3 player. Some allow you to browse the Internet, although not as fast. Some will read the text to you using a computer voice. Some allow you to add notes to what you're reading, or take notes on a blank page. It is a good idea to check all the features before you make your purchase.

By next Christmas, you can expect an avalanche of new brands of e-readers offering a wide variety of features, but today the market is dominated by three companies; Amazon, Sony and Barnes & Noble, and even some of them have trouble keeping units in stock.

Amazon's Kindle has set the standard for the e-reader market. The Kindle 2, about the height and width of a paperback book and the thickness of a Pop-Tart, has a 5-inch screen, while the Kindle DX offers a much larger 9.7-inch screen. Books are easy to read on the Kindle 2, while newspapers and magazines are much easier on the larger screen. Amazon is also trying to break into the school book market, and the larger format would work better there, too.

Sony produces e-readers of the same approximate size, while Barnes & Noble's Nook is comparable to the smaller Kindle, with a small, second color LCD touchscreen instead of the keyboard found on a Kindle.

None of devices are cheap. The smaller Kindle 2 is $259, while the comparable Sony Reader Touch edition is $299, and Barnes & Noble's Nook sells for $259. The larger format Kindle DX is $489, while the similar Sony Daily Edition reader is $399. A protective carrying case can add $25-$50 to the price.

Unfortunately, the Nook, Amazon DX and Sony Daily Reader were back ordered during the past Christmas season.

So what's the best choice among the popular e-readers? Since the Nook isn't even available until mid-February, there are at the moment only two choices; the Kindle and Sony. The Sony Reader Touch Edition and its $199 cousin, the Sony Pocket Reader, share one huge disadvantage: You can't download books wirelessly. You have to hook them up to a computer to download books. The Kindle does offer wireless downloads, and it works flawlessly. With Amazon's customer service and comprehensive catalog. The Kindle is still the benchmark for the e-Reader, although the Nook will be a strong competitor once it's available.

But both will soon have a lot of new competition. Keep an eye on companies such as Plastic Logic, iRex, Kobo and Wistron, which are planning to join the party within the next year. Time Inc., News Corp., Conde Nast, Hearst Corp. and Meridith Corp. are reportedly teaming up to offer their own e-Reader, too.

Other e-readers aren't the only competition for the Kindle, however. Many people are willing to read books on other devices -- their laptops, and, increasingly, on their smart phones. Amazon and its competitors have already released versions of their e-reader software for these other platforms.

This speaks to another disadvantage of the e-reader; it's yet another device to lug around. Many people willingly gave up their MP3 players, hand-held game consoles, cameras and cell phones in favor of a smart phone that does it all. Convincing them to pay for and lug around an e-reader is a tough sell.

Another concern is the decision by some major publishers to delay offering electronic versions of hot bestsellers until months after the print versions hit the book stores.

When Apple finally unveils its long-rumored tablet computer, that could also disrupt the e-reader market the same way the iPhone did to the cell phone industry. People may find that they'd rather read books and magazine on it.

So this leads us to the question; what's a frugal reader's best choice -- an e-reader or printed material?

To answer that, let's pretend you like to read the latest best-seller every week, the Wall Street Journal every day and Time Magazine each week. What are your choices?

If you shop locally and pay the cover price for your books, and buy subscriptions for the paper and magazine you'll pay $20-$30 a book, adding up to around $1,300 a year. Add the paper Wall Street Journal subscription ($258 a year) and paper version of Time magazine ($20 year; yes, they're practically giving it away) and your yearly tab would be $1,578.

If you buy them in Kindle format, and we assume your Kindle will last three years, then your cost per year would be $91.66. The bestsellers would cost $519.48 (at $9.99 apiece). Add the cost of the Kindle version of the Journal ($179.88) and Time ($17.88) and it comes out to $808.90.

That's more than $700 less than buying the same reading material on paper.

Of course, if you took the books out of the library and read the paper and magazine there, you'd pay nothing except the cost of transportation and perhaps a late fine.

What isn't factored in here, though, are a couple of the e-reader's greatest selling points.

First, with e-readers, you can buy a book 24/7/365, from anywhere and have it delivered into your hands in a few minutes.

Second, for the ardent bibliophile, books inevitably expand beyond the space allocated for them. And the first time you have to move that library, your lust for an e-reader will grow stronger with each box of books you lug up the stairs.

A major drawback to the e-reader is that you don't own these books in the sense that you could resell them or pass them along to friends when you're done. Half-Price books doesn't take eBook trade-ins. However, one appealing aspect of the Nook speaks to this; it will allow you to 'lend' a book to a friend for up to two weeks.

There can be a hidden cost to e-readers, as well. I found that owning an e-reader made buying books so easy that I purchased a lot of books that I would have normally waited for at the library, or borrowed from a friend, or bought used. Just as the convenience of credit cards entices us to overspend, e-readers can do the same thing to our book budget.

There are a few other minor advantages to paper books. If you're caught out in the cold, the Kindle, despite the name, won't help you start a fire. If you discover too late that someone has stolen the toilet paper in a public restroom, a Sony Reader isn't going to come to your rescue the way a paper book can. And for lining the floor of your bird's cage...

So what's our conclusion? Electronic readers can save money for people that buy a lot of new books. If you're comfortable with using the library, however, an e-reader could tempt you into unwise purchases, at least until more libraries offer more choices for digital downloads.

If you're still intrigued by the e-readers, though, we'd suggest holding back for a little while. There is a lot of competition in the pipeline that should drive down prices, and new products will be more versatile, too. We'd like to see more e-readers that accept a wider diversity of formats, so you can comparison shop for digital books rather than be handcuffed to one merchant.

In the meantime, you might try downloading a book or two onto your laptop or smart phone, and see how that goes. The best way to save money on an e-reader is to discover that capability in a device you already own.