When I first got mine, the battery ran down very fast. I plugged it in; the red "charged" light came on after about 15 minutes, but the battery gauge didn't show a full charge. It ran down again in a very short time -- 1/2 hour or so, <50 page flips. Same thing again with the charging -- the light came on quickly but battery didn't show as full.
The next time I charged it, the red light never came on (and hasn't since, even though I've had it plugged in for hours). The gauge shows a full charge and hasn't gone down since. I've been using it, but plugging it in every 100 page-turns or so just because I've been putting books into it etc.
I don't think this is a good sign, and I guess I'll take it back once they've got more in stock. Besides this problem, annoyances around the desktop application not doing much, and the complex process to get PDFs into the thing (which seem to be common e-reader issues), I really do like the thing a lot.