I was just finally shipped my Sony eReader, which I ordered a few months ago. It's the one with the "revolutionary" new e-paper screen, and the horrible Mac compatibility. I have yet to get it sync'd to my Mac, and I'm working on 2 options to do so: 1.) Running Windows in Parallels and/or BootCamp, and 2.) Installing a very convoluted open-source solution that runs on the Mac natively, but doesn't allow you to buy Sony's eBook format, but will allow you to install text and PDF books, along with a few other features. Once I get things syncing, I'll do a full review here and at Epinions, but here's my initial impressions.
Aside from the Mac compatibility issues (which I knew about when I bought it), it does really well. The screen looks great, though I wish the "white" were a tiny bit brighter (it's kind of a newspaper gray). The text is very clear, though a tad jaggy at times, kind of looking like the printout of an old inkjet circa 1992.
The e-paper screen is easier to read for long periods, I think. But the refresh rate is super-slow. It takes nearly a full second to flash to black then re-write the new page, and sometimes there's a little ghosting left behind. Still, not that much longer than physically turning a page, so it's a wash.
I really like the interactivity features for clicking through to endnotes, etc., and you can click on what you want to go to in the table of contents, which is nice (almost like a web page!). I bet this would be a great platform for the revival of Choose Your Own Adventure stories.
I did try the MP3 player features, and it presents a nice black-n-white version of the album art while you listen, and the audio quality was very clear. I'll have to do a blind taste-test top be sure, but I think the audio may be cleaner than what's coming out of my iPod, with less amplifier noise.