The Sony PRS-600 is my first and only ebook reader too. I love it and I even decided on it sight unseen.
It can read PDFs you make as well as free epubs and even .rtf files. It can read any DRMed books as long as they are from the Sony store, or they use the Adobe DRM, providing you have authorized the reader with Adobe Digital Editions. So no Amazon or Barnes and Noble ebooks if they have DRM (there's no way to tell till you buy and download it, so best not to waste your money).
I think books from any other source besides Amazon and B&N will be usable on the Sony Reader.
The Borders ebook store used to just redirect to the Sony store, I don't know if that is still true.
One more thing: You can trick the Sony store. Say you are in the US when you download the software. I think you also have to use a credit card with a US address, but you might be able to just put some random address and skate past that. People say bad things about the Sony software but their store is good for bestsellers, and I haven't had any major issues with their software but one, which I won't scare you with now but you might find out about it later, since it seems like everyone does.
Last edited by banjobama; 07-07-2010 at 05:06 AM.