I like the idea, it's like uservoice, getsatisfaction etc only really really simple.

My only complaint is the fact you've called it 'dropbox' most people associate that word with a file storage/sharing device (such as getdropbox.com or the OSX dropbox).

Perhaps 'comment box' would be more appropriate?

Also, you may want to add some flood control - I was able to bombard my test account with all manner of crap ;)