I just looked in my "temp" folder (on Windows) and there's hundred and hundreds of temporary folders in there created by Arduino.
Mostly they have names of the form:
console482066375975536426.tmp
untitled6038223369510823977.tmp
These really ought to be cleaned up...
The other problem is the build folder. Sometimes I get the message "build folder not found" when compiling and the sketch refuses to compile. This can happen over and over...to the point where I now have a batch file on my desktop to create the folder manually (at which point it always compiles perfectly).
I've tried setting a custom location, I've told the antivirus to ignore that path, nothing seems to make any difference.