I really like Live Mesh. I had been hoping/waiting a long time for Microsoft to bring out a free tool that allowed me to store all of my documents online, and have them sync automatically. I had previously tried other options like xdrive.com or box.net but never liked them because they either looked too 'clunky' and dated, or too dumbed-down and over-styled.
I use Live Mesh to store copies of my files, but something that I find really useful to do with Live Mesh is to store handy applications in a folder I have, and have that folder sync itself to all of my other machines and to the cloud. Of course, you can't just put any application into the folder because unless it is installed on each computer it won't work properly. However, if you head over to www.portableapps.com you'll see a whole bunch of applications that have been packaged up especially so that they do not require installing. Just unpack the contents of the file you download for the application to your Live Mesh folder and run the executable, simple!
There are all sorts of applications available, everything from an anti-virus scanner to a full office productivity suite! My favourite is KeePassPortable as it allows me to store all my personal information in an encrypted and always-accessible way.