I saw your short demo at BarCamp and I must say Dropbox looks great! Are you planning on having a Linux port as well, or is too early to talk about that?
Also, as another SFP applicant I have to tell you that I really hope you get the funding - you deserve it.
a linux port is doable (mac will come first) -- everything's written in python and was designed from the outset to be portable. although this isn't the initial focus of dropbox, a linux port would be interesting for maintaining small web sites or web apps -- instead of using scp/sftp or equivalent you could just modify the files on your desktop and have them synced to your web host.