The latest iLiad's have a larger battery, which lasts at least 10-12 hours.
Note that no current E-Ink device will read Adobe secure e-books. The Sony PRS-505 MIGHT be able to read these when the announced Adobe Digital Editions software upgrade becomes available.
Adobe's own PDF reader also no longer reads e-books, so if Adobe Reader version 8 (e.g. on Windows) can't read your documents then neither can the iLiad.