Are people using Dropbox on servers, though? A lot of the benefits of Dropbox don't strike me as helping for servers, for the most part. I don't have too much experience, but it seems to me servers are one place you have to actively manage your backups, and can't rely on the "it just works" philosophy of Dropbox.
I think I'm more likely to pay for a service like Dropbox on the server than on my desktop.
Reliable backups are a big deal on a server, and maybe not as much on the desktop. I mean, I'm not too fussed if my mp3 collection gets stomped by a hard disk failure (I just download it again from emusic), but if tens of thousands of forum and ticket tracker posts are lost, I'm gonna be devastated. And, having it in a shared location that makes it easy to copy the database and website to a development machine might be cool. (I'm kinda talking abstractly here, as my own products provide tools to solve all of these problems in different ways, but they're things I've had problems with in the past. And, if Dropbox had a server product, we'd probably add it as a backup target option.)
Not many are using Dropbox on servers yet, but if their users upload files, they should.
My itty bitty part-time startup has a better uploader than Flickr, thanks to Dropbox on the server. Users share a folder with the server and copy photos into it that they want uploaded. They can be choosing photos to upload even with no connection, e.g. traveling with a laptop.
I think there's an audio site out there using Dropbox this way. Other than that I haven't heard of it. Maybe when their API includes folder-sharing functionality more people will do it. Right now I manually accept the shared folder request.
I share folders on server with other Dropbox users (developers, designers). For me it's better alternative than webdav, ftp or scp. They work localy and everything syncs between them and to server plus it has some version control.
I would even use it commercially in my products but API lacks ability to share folders. For now you have to do it manually.