Sounds great for people that already have dropbox, for others that might not work so great. Most savvy computer users understand dropbox, but sometimes (less savvy users) just can't get it to work.
I wouldn't make it the only upload method, but I highly recommend it at least as an option. And with 25 million users, there's a good chance a lot of your new users already have Dropbox, especially within the early adopter crowd.
