Safari :: MBP Freezing Up - Cannot Move Cursor Around Screen

I have a 2009 13 inch MBP with 4G of RAM. Its loaded with the current version of Snow Leopard, version 5.1.5 of Safari and version 4.5 0f the Mail App. The screen of the MBP freezes up 3 - 4 times per day. Ninety percent of the time Safari is open when this happens (some of the time, the Mail App is open as well. The remainder of the time I may have another browser open, but the Mail app is open. I can move the cursor around the screen and "force quit" any open applications except Mail and Safari when this happens. The icons for Safari and the Mail App in my Dock turn grey if I click on them. Otherwise the spinning pizza wheel shows up. I have to use the power button to turn off and restart the machine.

I have tried resetting the PRAM. I also got a couple of error messages concerning Hazel (v3.1.1) via Growl on one occasion. Simply stated that there was an error when Hazel started to run, checking .docx files for Music and video. (Hazel runs from startup and I have rules set up to remove partial and duplicate downloads and clear all Trash files within a set period). I uninstalled Hazel, but the freezing still occurs. The apps I have running most of the day are Mail, a browser, Omnifocus, Preview and either Pages or Word in Office for Mac 2011. I back up a couple of times a day using Time Machine and every couple of days update a copy of my hard drive using Carbon Copy Cloner.

Info:
MacBook Pro, Mac OS X (10.6.8), Safari (5.1.5) Mail (4.5)