I can understand about there being limits to the number of books. The devices are small and have to work with a limited amount of memory and storage. Some readers don't even offer an SD card slot, so you're stuck with 1-2GB at most.
Most books are below 1MB in size so to fill 10GB you'd have to have tenthousands of books. What have you on there, the entire Project Gutenberg? Is that even 10GB?
I've been using ereaders for a year and I still don't have a hundred ebooks yet... total size below 50MB. I probably won't be able to fill my 2GB SD card for another decade... well, maybe with comics it's a different story.
It shouldn't hang up in any case, though. If it comes across an invalid file or I/O error it should display a proper error message instead so you can fix/remove the offending file or replace a broken SD card. I hope they will improve on that with a firmware update.