osx freezes when log into one account

I just upgraded to the latest security update of 10.8 last night, told it not to reboot (clicked "later"). After declining to reboot, immediately shut down (not rebooted) Macbook Pro for the night and went to sleep.

This morning, I turned the computer on. After logging in, I have a couple minutes (or less) and then the computer irretrievably freezes. I tried multiple times, same deal. Booted up without loading the previous windows. Still freeze. Stopped all auto-start programs, still freeze.

Repaired disk and partition. Plenty of time, no freeze in the recovery mode.

However, after logging back into my regular account, the freeze issue persisted.

Logged into my wife's account - no freeze issue. OK, so maybe just my account. So I went to System Preferences, hit the unlock button and escalated privileges with my main user/pass and created a new account. However, maybe 30 seconds later, the computer froze irretrievably again. Mouse and keyboard do not respond. Typical animations on the screen have frozen, so it's not just the input devices.

Forced a power off and then booted into the brand new account. Thirty minutes in, still no freeze! This is great, except I had the other account all the way I wanted to and would rather just figure out and fix whatever's freezing up.

How might I do this? I can't find reports of mass problems with the latest security update online. I'm guessing it's a confluence of something in my config plus the latest update. How should I go about diagnosing?

For right now, going to Apple Store is not going to happen (for a variety of reasons, chief among them time, distance, and general daintiness of my poor old and decrepit laptop!).

Thank you!