I bought the 350 (awaiting delivery) primarily for my oreilly books. I think having had a kindle you will be happy if you adjust your expectations. I had a kindle and have a dx. the thing is, even thought the dx is better for reading, it still comes nowhere near the experience of a book. Let me ammend that...it is not great for technical books but fine for getting lost in a novel.
The reasons then that I have gone for the smallest reader (the 350) and for the sony are as follows...
1) you can never get the same experience with an ereader that you would with a technical book so accept that and get somethng really portable and think of it as a supplement. A reader to pull out of your pocket on a line or while double parked to keep your skills fresh.
2) after using the clunky kindle keys to navigate I realized how important touch is to accessing the toc. For me technical books are nothing like paperbacks and require constant jumping around. also the ability to flip through pages quickly is a real plus.
3) finally (if it has not changed) remember oreilly lets you buy ebooks for $4.99 if you can prove you own the actual book.
Aanyway that is my reasoning for getting the 350. I hope it does not let me down