No problems for me, and I've had it for a month. I've read four books on it, one of them a huge 700-pager.
Well, one time my Kobo froze (stuck on one screen with the blue light flashing) while opening a book. But a quick poke of the reset button fixed that.
I've never been upset with the battery life, nor have I noticed it running out faster than it should. Overall, it strikes me as a very sturdy and reliable device.