hi all - been lurking for a week, great info on this site obviously, and I just bought a prs-600 after perusing the reviews and pics. I thought i'd drop my 2 cents about it having played with it for about 6 hours now.
--I took the big plunge into ebook readers, this is my first one. Bottom line: love it, am keeping it.
Now for the nitpicking:
--its on the pricey side. I paid $295 (after coupons, and after taxes) at staples. Plus $23 for the neat cover (from borders, after coupon). To compare: the kindle 2, refurbished, sells for $219 on amazon right now, and new is only $249. Plus there are tons of new readers coming out in the next 6 months, will drive price down further I think. So ya, I overpaid.

Tho its nice to just have it now, with the technology evolving so rapidly there really isnt a good time to buy. I'll upgrade even this within a year I think, maybe sell it off on ebay sometime next fall.
--I chose the sony over the kindle or the nook because of pdf/reflow capability, the variety of ways to annotate, file format flexibility, and touch screen. I plan on getting ebooks out of the NYPL too. Before buying I visited the sony store in manhattan, and the non-touch screen prs-300 really did have a better screen (its uncanny how much like paper it is), but I want and need features like annotations etc.
--I like it a lot and I believe I'll use it a lot. That said, many features on it really need work.
--in low-light situations you really wish the contrast was better.
--sony software (ebook library) took a while to figure out. I kept erasing files on the reader by accident (while 'syncing') until I turned off auto-syncing and just dragged what i wanted manually (within the software). Its not like palm pilot syncing where you can tell it what direction to sync in. The "collections" feature is nice, gives a basic way to create 'folders'. Nested folders would have been nicer.
--writing with the stylus - its good, and annotation is the best feature of this sony over competing models (can highlight, bookmark, add note to the bookmark/highlight, take typed or freehand notes, draw anywhere on the page, or take a note-to-self). But -- I always feel like I'm about to scratch the screen with the stylus. It feels like it 'digs in'. Havent seen scratches yet tho. But I don't want to put a protector on the screen cuz that will add yet another layer of dimness. So I used an old palm pilot trick: I wiped the screen down with some silicon spray. Now its *slick*

(Silicon spray is non-oil based, its 'dry'). The stylus slides around like on an ice rink. Much nicer to write with.
Mostly i'm using freehand annotations, since the pop-up 'keyboard' leaves a lot to be desired. I mark up my pdfs and books freely, and then transfer the marked up document back to the pc, and within the sony software you can jump from markup to markup easily, and from there I get my comments into the word document i'm working on. Its actually straightforward and I wont have to carry a ton of printed pages around anymore.
--I *wish* they would sell french-english dictionaries. The double-tap look-up feature would be so beneficial to language-learners if sony just sold multi-lingual dictionaries.
--The 100 character transfer limit on highlighted text, is frustrating, but I guess its understandable. They dont want people stealing the content with copy/paste. I guess if it were a real book we'd have to type in the quote ourselves, and I guess the e-readers are trying to mimic some of those limitations for the sake of DRM.
--wish it had more "dedicated hardware buttons"; specifically:
Home, Back, Font size, and frankly I wouldnt mind a physical keyboard like on the kindle. And maybe even hardware play/pause button for the mp3 player.
--wish you could reassign the existing buttons' functions.
--love the massive (32gb) storage expandability. (16gb on each slot, technically).
--the user manual is worth going thru, there are some on-screen shortcuts that are handy.
So far so good though. While I over-paid for it, the kindles (either 1 or 2) were out for me because of their limited storage, limited annotations, limited file formats (i know hacks are out there but thats an extra step), etc.
Thats it for now, still playing with it.