Right now all I think I know is that it has a 6" E-ink screen, 2GB Flash, 3G, and Wifi as well as support for XMDF, Epub, and PDF. It's going to be available in December (only in Japan, of course).
via Akihabara News
Update: Crunchgear had more info on the Biblio Leaf:
Toshiba says buyers can expect a built-in calendar, a calculator and a notebook function. The Leaf’s internal memory (2GB) can be expanded via microSD cards (the device also features a microUSB port).
What’s pretty interesting is the mini solar panel that’s built into the bottom right of the device. Toshiba doesn’t specify how powerful the panel will actually be but says that with the internal battery fully charged, users will be able to turn about 7,500 pages consecutively.