About once a month.
A couple of times a day when I'm online much. I use CCleaner and it cleans everything up nice.
I rarely do it and have to do it now.
Two to three times a week .
Whenever I think of it (maybe once a week).
HA! I do it a couple of times a day with CCleaner and Glary Utilities. After I was phished? I keep it as cleaned as possible.