Actually, it was on a vacation hood - in France. In Normal Hood, it works fine again. Huh.
I noticed this yesterday with a sim in Egypt. I had set him to "Collect Dig Sites" with SC and my game would seemingly suddenly start to run at a crawl at random as you described. I finally figured out that it was happening when he was trying to reach the unreachable excavation sites on the small island there.
The action would queue up, it would get the blocked thought bubble, and then re-queue. Anyway, whenever those particular sites which he could not reach became the 'target' for SC, my game crawled almost to a halt. I'd pause the game, cancel SC, teleport him to the island to clear the excavation sites then pop him back onto the mainland and turn SC back on. Stopped the freezing completely. It's an easily reproducible error. If you set a sim to that task from the expensive Egyptian house those are the first sites the sim targets.
I'm using 1.24 final and have the all expansions and stuff packs except pets. Game is patched to 1.24. Date on Awesome.package is 10/18/11 at 10:14 AM.