It's Friday afternoon, and this is so destined to be an off-topic post...
Here's the thing. For the last year or so, I've been the proud owner of a Sony PRS-500, a gift from my beloved wife. Awesome, awesome gadget.
In case you are considering getting one, here are some of the good things: very low battery consumption; doesn't heat up; very lightweight; reads non-proprietary formats (plain text, RTF); excellent clarity for reading. Reading quality, weight and battery consumption are the things that won me over.
On the down side, it doesn't deal very well with most PDFs out there, and books with images will typically become unusable after they go through the reformatting. Plus the available books to purchase are limited, although the selection keeps growing.
As a last tip, if you are exporting your own documents to read on your PRS when you're on the go, I've found that font sizes of 11 to 16pt work best for me. I always enlarge the font for maximum readability as well, but I guess that's more of a personal preference thing.