Personally, I have disabled system restore on all except the OS partition (C:\ ). I install all software on that partition, and, of course, that is also where the registry resides. My documents are on a separate partition on a different hard drive (and backed up to an external drive as well).
In moving some data around on some non-boot disks on my XP desktop, I was able to see that XP stores some restore point information on these "auxiliary drives" -- including USB drives.  Is there any reason to have restore points on any drive other than the boot drive?   It is possible to deactivate the restore feature selectively for individual drives.    
Restore points and data