Here's something I've been using for some time now, and I think it's great - FolderShare. It's a way to selectively exchange files with users that you invite (versus using a global P-to-P type of sharing where anyone can see your shared directory).
It is owned by Microsoft now and is still in "beta" even after a couple of years, but it works without a hitch. Almost. (see below)
I have a directory on both my home and work machines that are connected in a "library". When I find an interesting utility that would be useful at home, I put a copy in that folder and the transfer happens automatically, in the background. Naturally, the sending and receiving machines have to be running the FolderShare program, but I rarely turn off either machine.
Not only that, but you can have multiple users sharing the same folder. It's kind of like RSS for files, only you control who can 'subscribe' to the directory.
One of the really nice things is that it works behind just about any firewall because it's port 80 based!
Now, the hitch. In theory, you can visit the web site and browse another machine's shared directories (the site is password protected, of course). If you click on a particular file, it will initiate a file transfer. However, I have had only mixed success with this. Sometimes it will just sit forever, sometimes it will timeout, sometimes you get the file. Size (in this case) doesn't matter.
And in my case, the chums who control the firewall have added this site to the blocked list under the category "Peer to peer sharing sites". I've put in a request to have it unblocked, but it looks like they won't do it. But the folder sharing auto-transfer feature is just great and works flawlessly.