I'm shopping for my first eReader.

From looking around online, I like the look of the Sony readers. Obviously I'd like to handle one before buying, though. I'm also checking ebay and craigslist. I'm seeing a PRS-600 for $100. How does the PRS-600 compare to the PRS-650 and also to the PRS-350? The 650 looks like it's significantly more expensive than the 350. What are the features that account for the higher price?
What are the things that you love and hate about the various models?
I don't think I need wi-fi since I work on a laptop all day and would have no problems downloading books while working. And I'd like it to fit it a purse but not be teeny-tiny. I read pretty quickly and I'm concerned that constant page turns will be annoying.
Thoughts, suggestions and comments are appreciated!