Well, I once had one F80 and I still own the F100!
Differences? Of course, there`s a difference in the price tag to start, construction materials, ergonomics and the AF module used, to name just a few.
The F80 is a very nice device, sillent shutter, acceptable AF (Cam 900), small size and light weight, making it a heck of a street shooter.
I prefer the F100, but, the F80 is just the best value for the money on that specific segment in the market.