There is currently a bug in the Windows devprev client which is causing temporary files to not be deleted when they should. This is causing Foldit to take up more and more disk space (quite a bit for some people). It is recommended that if you are on Windows, you revert to the 'main' update group for the time being. We are working on a fix for this, and should hopefully have it out soon.
Mac and Linux are unaffected by this bug.
http://fold.it/portal/node/993082
scroll to the bottom, to see the 'main' log.txt
On windows:
run cmd
navigate to foldit directory
ie:
c:
cd \foldit
then run this command (paste to cmd and press enter)
for /f %a in ('dir /s /b *.tmp') do (del %a)
It will kill all *.tmp files in foldit directory and all subdirectories
In Windows Explorer (not internet explorer :) right click on Local Disk (C:) - click Properties from the flyout menu.
A dialog box will pop up showing how much free and used space you have on your C drive.
Click Disk Cleanup button - this will take a bit of time to run and will then show you a list of items with checkboxes and the file space you can recover by deleting them, if you click an item an explanation of what it is will also appear. Deselect everything except temp files - I had 2.3GB - and click Ok.