Brilliant thread, have enjoyed reading through it.
I've had my 600 for a week and have read 4 complete novels plus 2 half-read books on it. This is far more than I would normally read with "treebooks" as I'd normally get through an average of 2 of those per week. It's simply much easier to pick up and put down (especially when reading more than 1 book at a time) and you don't have to worry about where you got up to as the reader does that all for you.
I spent a long time deciding between a 300, 600 or a kindle. I wasn't comfortable with importing a kindle from the US to the UK in case something went horribly wrong - be just my luck. And I thought the 300 screen might be a little too small with the amount of reading I do. So I think I made a good choice, although (being so impressed with the sony) I'm very tempted to also buy the 300 for holidays and travels ...
I don't think the 600 is 100% perfect but I'm not convinced that any ereader currently can claim that. I think it's just a case of trying to work out which one will suit you and your reading needs best.
My husband was interested in an ereader but wants one for reading technical pdfs and in colour - but I think he'd be better off not with an ereader but with a netbook for that from what I've read on this forum.