It depends on the quality setting on your camera, on how many pictures a thumb/flash drive will hold, as well as the size of the drive. I take pictures on the best quality on my camera and they take up a LOT of room on these. I filled my 4gig flash drive with about 300 pictures....
I went to storing everything on Carbonite, an online service, it automatically uploads all of my documents and pictures for around $50 a year. I can access them from any computer or internet device, and if my computer should crash, I can re-download everything.
I do use flash drives for transferring data from one computer to another, but like your computer's hard drive, they can fail....