Are you using Live Mesh ( www.mesh.com ) to sync your files between multiple devices?
I am! It is a VERY usefull service. But recently i noticed the free space on my hard drive was going strong towards, well, zero.
In researching why this is, i ended up in the folder:
C:\Users\ YOURUSERNAME \AppData\Local\Microsoft\Live Mesh\GacBase\HoldingArea\
This folder had no more and no less than 85 GB of data in it. Old files that either i deleted from mesh folders or synced.
Make sure your devices are synced and no transfers are in progress, if they are, let them finish, and delete all the files in this folder. FIXED!
The service is still beta, so i guess they need to fix this in the release version.