I have about 120 right now, and growing.
I do have an sd card-8gig. I haven't even scratched the surface of the space!
I like to have all my books with me. I never know when I'll be stuck somewhere waiting and want to read, but I don't want to read a classic, I'm in the mood for a mystery.... The possibilities are endless (sort of ) when I have my whole library right in front of me.