Dropload Hits 55,000 users. That's a lot of people.
Jon has pretty much taken administration duties over there and added lots of neat features which I think has added to the growth. You can see the files you've dropped and are given the chance of resending the file in case it wasn't picked up by the receiver.
When I first came up with the idea for Dropload it was because I couldn't trade files with my friend Sean over AIM. The trick about coming up with web ideas is (I think)–when faced with something you can't do in your daily work–rather than solve the problem for yourself, solve it for others as well. But don't get bogged down in the implementation because you can architect the greatest Dropload web app of all time and very few will be able to use it or understand it or care.
RSS used to be like that until people were educated and the little orange XML buttons disappeared (or at least don't give you XML when you click them). PGP is definitely like that. I would very much like to solve the PGP problem because I think it's something people don't know they need. If there's an idea there, it'll present itself I think. Sorry to ramble.