Like many, I've been experiencing a lot of problems w/ my phone slowing down since the ICS update.
Just yesterday, I purchased an app called Fast Reboot Pro. So far, I think it was a good buy. I've been using it for a day and a half, and it seems to have fixed my issues in a slow phone, rather than doing a full reboot.
If you're willing to spend a couple of bucks on the Google Play market, check it out and see if you like it. You can add apps to an exclusion list, as well. That is, exclude which apps to have shut down when doing a fast reboot.