From my point of view, I would say "Buy a Kindle instead of a Sony Reader". But I'm a bit partial.
I hate Sony, since they have never improved the ugly firmware of PRS-600. I bought a Sony PRS-600 in November 2009. This device was (and is) completely unable to manage large libraries. I've stored around 1200 books in a 4 GB SD-card (tha was only 1 GB). You need to know that the PRS-600 had to be connected to the computer, in order to charge the battery. Each time you deconnect it (once charged),it spends 5 to 6 minutes to sort the library, even if you didn't modify it. Did you want to add one or two books, in your SOny, Ok, let's go, and another 5-6 minutes to sort after being unplugged. And this operation was very bad for the battery.
Another default of the product was that the battery life quickly lose autonomy.
AND SONY HAD NEVER UPGRADED THE FIRMWARE.
A lot of all this complaints are now solved in the new PRS-650, but the early adopters of the 600 have been forgotten, it's a shame. So I think I will never buy a sony device.
So, this year (well, last year, in 2010), always in November, I buy a Kindle 3 (after having taking advices of Kindle 3 Owners), and that's happiness. Sorting of Library is very quick, and done only when necessary. You can use the Kindle 3 when plugged to the computer when charging (you couldn't with Sony). Contrast is much better than the Sony. I convert all the ePub books and all is well.