I installed my current Vista64 on my 37GB C:/ partitino back in July.
With time the C:/ got used up after i kept installing regular usage softwares like MS Office, Macromedia products (nothing useless just 'required' products) etc, etc.
Uptill last month the only thing left with 1GB or so. and I was stuck with getting low-disk-space every hour. Anway i expanded the damn partition to 80GBs+ now. and vista is cool
Btw vista's hibernation works like charms. Saves load-up times (caz it takes that time while going to hibernation) Only problem so far, my Sony Ericsson K790i's internet conection has to be disconnected before the hibernation can proceed.