Ok, guys, the answer is simple. It's an app. You've downloaded something that is clogging things up. We've all done this. There's a power that takes over our mind and we go searching Google Market for new, cool apps. Then we start scouring the web for tips on new apps. Then the Amazon market, then Getjar. It's an obsession. We download almost anything and everything trying to fulfill the need to try something new.
Eventually we'll download an app(s) that starts eating the battery or the GPU or the CPU or bandwidth. It's inevitable. I've done it, you've done it, we've all done it.
There are only 3 options:
1) Start deleting apps until the problem goes away. This is problematic as it's entirely possible that it could be multiple apps not playing nice with each other. It's a hit and miss solution.
2) do a factory reset. Then carefully install apps, never more than 1 per day, to determine what app is causing the problem. This will solve your problem EVERY TIME. Alas, it takes a lot of discipline to do this but it will work.
3) Do nothing. Learn to live with the sluggishness and blame it on the phone or ICS or the gods.