Windows Live sync used to be called Windows Live FolderShare. I have now been using this free service for a few weeks, and I must say that I am impressed. It synchronizes central folders (mainly ConnectedText Projects) on my Home, Office, and Netbook computer without the slightest problem. I never have to worry about whether my files on any computer are up to date. It does not store any files on the net.
You have to sign up for Live sync. It's part of the Windows Live suite.
I have also used Sugarsync and Dropbox . Live sync is more intuitive and faster (or so it seems to me). Dropbox is not really an alternative as it forces you to put the files or folders to be synchronized into the special Dropbox folder. But I do believe the two are complementary. So I use both: Dropbox for text and doc files I am currently working on, and Live sync for ConnectedText's Project folders. As I said, this system works like a charm.
Apparently, there is an application in the Powertoy suite called Synctoy that offers a GUI for this. But I have not used it.
Live Sync is supposed to work with Macs as well as PCs, though there seem to be problems with Snow Leopard.
1. See Windows Live Sync vs. Live Mesh vs. SkyDrive: Which is Right for You? for a discussion of the relative merits of each. I myself don't need (or perhaps better: want) storage "in the cloud."