Since getting a W7 computer, I notice that there seems to be more temp files (%temp%), and the folder doesn't seem to eliminate them itself. I've been going through them now and then, and deleting anything over a month old. Even now, it shows as 376MB in Disk Cleanup and has over 200 files in it.
Having a SSD, I try to keep it free of anything not needed.
I do run Disk Cleanup each night and always check the boxes for Temp Internet Files, Offline Web Pages and Recycle Bin, but rarely anything else. I'm never sure if it's OK to completely delete all the Temporary Files.