I upgraded to OS X Mountain Lion on my Macbook Pro last year, and since then I’ve had no end of grief with the machine locking up with the beach ball of death. I was ready this morning to do a fresh install of the OS or even roll back to Snow Leopard–but in a last-chance attempt at resurrecting the installation I did a couple of things. One of these was to clear out the applications folder including the Flash installation.
The other thing I did was to go into the recovery console (hold command-R at boot) and repair the disk permissions on the drive. The list of repairs was extensive–possibly it was a legacy from the Snow Leopard upgrade.
Taking these actions has removed the cruft of unused applications and so far I’ve not seen much of the beach ball. For anyone else thinking about something as drastic as wipe and reinstall, maybe this post will save you a morning. I’ll update in a month or so.