I just spent a full day trying to figure out what was causing my sessions to get corrupted and the general system instability. I believe it is a combination of a hard drive error and outdated plugins.
Everyone follow along at home:
Check all your drives for errors.
Install the latest version of Pro Tools, 7.4 cs4.
Run the digidesign plugin updater. http://www.digidesign.com/index.cfm?langid=100&navid=54&itemid=28250
Check all your other plugins to verify they are up to date.
Since someone geekier than myself has requested graphs and charts etc for the mic shootout, here they are. I used Sigview for the spectral analysis, I have no idea if I did it right, nor do I care about the results. I use my ears.