DropCopy: Useful.
Sure, you can install Mac OS X Server on one of your various Mac minis or turn on FileSharing on each machine in your network, but if all you want is a simple way to send files to other users' desktops,
DropCopy 1.01 is the way to go. The little utility is free for smaller networks and personal use (25 USD for larger networks) and should be installed and run on any Mac. There's one feature that makes me shiver a little, though: It lets me copy other users' clipboards. I'm sure they've covered the security issues about this in the preferences, though. If not, wait for the next version. ;)