DropBox is one of my preferred tools these days. One usage which is not obvious, but makes a nice hint is to use it to distribute a new software disk image to my different computers (we have six of them in the family). I usually download new apps on my MacBook Pro. After I install the app there, I put the disk image in my DropBox. You may wonder what is the gain, given the disk image has to get to the DropBox server first.
Well, this may not be obvious at first, but DropBox uses a very smart filesystem (I think these are called hash filesystem). If the file to be uploaded is already on the server (even in some other person's account), then the file is not uploaded, and your "server" copy is instantaneously available for other computers to download. Try it; it is impressive. Basically, there is only one copy of each file on their server, which is pretty smart.
So in my case, most of the time, the disk images are already on the server. This morning, for example, I uploaded the last VLC and Skype disk images, and bingo, they were both on the server in a second. Then, when I log onto my other computers, these disk images are automaticaly downloaded to be used for installation (if you have left your session active, they even get downloaded in the background).
Of course, if you are on the same network, it may be faster to just drop the file on the various computers ... but in the end, it is usually more work than just using DropBox.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091002011616876