I'm still in the decision making process so I have no ownership experience to share, but I did spend about a half hour playing with the live display models of both the 300 and 600 today in my seemingly never-ending research.
In my opinion, giving the 600 a 1 out 10 rating is harsh and unwarranted. The 300 is definitely crisper, but from reading some criticisms of the 600 screen, I was expecting the worst but was very pleasantly surprised. I didn't think it was too bad at all. Perhaps not the best, but if I was to rate it, I'd say at least a 7 or 8.
The look and build of it are by far the nicest of any reader I've seen. It's very elegant and refined. The interface is wonderful and extremely functional. Perhaps it was because I didn't have great expectations, but I came away feeling quite positive about the 600.