Coming from the mobipocket world, I did miss the dictionary function at first. Except that every REALLY difficult word wouldn't be in the limited mobi dictionary I had anyway (not to mention the foreign-language books). Quicker to whip out the blackberry and grab a definition online.
There is a dictionary hack for the PRS-505, as I am sure you are aware, but I haven't tried it.
I've always been format-agnostic - as long as I can freely convert from and to a format, I couldn't care less (I hope Kovid is still working on lrf2html or I'm hosed
). I avoid DRM-based books on general principles.
Maybe in a year or two I will wish for the user-replaceable battery, but odds are by then I will have gone for a color model
Different strokes for different people. If the Iliad was lower in price, I might have bought that.