[full disclosure, I work for Microsoft.]

Do you have a home computer and a laptop?  Or perhaps a mobile phone running windows mobile along with a computer?  How many different computers do you spend your time on.

Me?

Five.

Two home, two work and my mobile.

Do you want to keep your documents synchronized across that varied landscape?  If the answer to that question is yes then Windows Live Mesh is the answer for you.

How mesh works:
There is a website that you login to using your @live.com email address, http://mesh.live.com.  It becomes your online desktop, the center of the wheel of your devices.  You then download an application to all your other computers that you want to sync with and sign each machine up to the same account.

Once that is done you may create a folder as a mesh folder and the contents of said folder will be sync'ed across all your devices.

It's cool.

Listen to this scenario.

I downloaded the mesh app to my windows mobile phone.  I now have the folder that stores the pictures from my camera phone sync'ed with Live Mesh.  So when I take a picture on my camera, the picture is automatically sync'ed across all my other computers.

Sweet.

Caveats:
You only have 5 gigs to play with for free, so sync'ing your music isn't an option (and any other large media files).  But for personal documents, such as all my writing, it is perfect.  I can pick up any of my writing projects on any machine and just write.

Also, I do not sync my work stuff on my personal pcs.  That is just common sense.