As far as displaying text, there should be no difference between 4 or 8 shades. (Text is black--only one shade.) Like JS Wolf says, you'll notice a difference if you're viewing pictures on the reader. I wouldn't expect there to be a really noticable difference in speed between the 4 or 8 shades, but there probably is a minimal difference.
Jerryprism--no e-ink device is going to have a back light. Backlighting won't work with the technology. You can get a Sony 700 that will have side lights--that's the only e-ink device with lighting actually built in. And as Kelly says, the Sony also takes SD.
As far as replaceable batteries go, for me that's a non-issue. I've had my Sony 505 for 15 months now, and still get three to four weeks out of a single charge--that's with reading between one and five hours every day on it. I do know that there kits to replace the battery out there as well--but don't have any specific knowledge of how easy the battery is to replace.
dordale
