Personally, IE or no, back when I used it a lot more frequently I would format and reinstall every three months, as opposed to six. Now I use it once in a blue moon, so my windows partition has been known to last as long as six to seven months.

The primary reason behind this rigid schedule of destruction and re-creation was cleanliness. I am not John Q. User who just uses office once in a while. I play with shit, I experiment, and my machine ends up looking like a recently autopsied corpse. Wiping the slate clean every so often lets me keep things running at least kinda smoothly.