Frequent blank screen/freezes/crashes with OSX Mountain Lion

I updated to OSX Mountain Lion a few weeks ago. Now, after startup, my computer continuously gets slower with the number of applications that have been opened (even if I have closed them after I'm done with them) until it finally goes to a black screen where I can only see/move the mouse but nothing else- I don't even get the SBBOD. Ultimately I shut it down because its unresponsive. After rebooting, it most often tells me the culprit applications are either Safari or Adobe Reader, but occassionally its others like MS Word, iPhoto, and R. I'd like to think my system is powerful enough not be slowed down by such trivial applications (15" MBP Early 2011, 2.3 GHz i7, 8GB RAM, 256GB SSD). On a side note, I've upgraded to both OSX Lion and then OSX Mountain Lion without ever doing a clean install- if that may be an aggravating factor? I thought disk space might be an issue so I downloaded MacKeeper to clean up my HD. While it recovered a lot of space on my HD by removing duplicates it hasn't done anything to improve this situation. I've also used the disk utility to repair disk permissions and repair disk. Any ideas? Should I call Apple?

Other symptoms:

-iStatpro and other items on dashboard screen are always extremely delayed

-I can tell its going to happen soon when pressing command+space doesn't open the spotlight menu. But when I look over to iStat it says its running at normal T, fans are turning fast, and there ~3-4 GB RAM free...