My C:\temp is so full of stuff, some unknown amount of which turned out to be not as temp as I first thought, that I've now had to create C:\verytemp for the really temp stuff, which I make sure is emptied daily.
Some 20 years ago, when HD space was at a premium, I wrote a small script to clear out various temp directories in Windows 98. I tested the deployment on a colleague's computer, only to have him inform me that he used c:\temp as "temporary storage for projects I'm working on". Oh, well.
I actually have a tmp on my desktop for this very purpose :-)
If you go back far enough then calling GetTempPath() from the win32 API would return C:\Temp. It was always meant as a place for programs to put temporary files, not for users to stuff their garbage.