I am, with trepidation but hope, posting from the main computer. Just prior to everything completely spazzing out, he'd had me move the "caches" folder to the trash. He was trying to move some other stuff, but I couldn't do it because of the spazzing. So he had me immediately shut down, then consulted his experts, then had me restart normally and do a "capture data" which gives the techs there all the info they need to troubleshoot. We had to re-update some stuff because doing the reinstall didn't do the latest batch of updates, including Safari. So, all that got done, but happily none of the spazzing crap was happening. We slowly began opening stuff like iTunes and iCal and Safari and twenty minutes later thing were still fine with no evidence of spazzing out. So, even though it would surprise him, he began to feel that the caches folder that we trashed may have been the problem. We'll know tomorrow after they look at the data capture - if they come back and say there was something corrupted or weird in that folder then we know.
The only thing wrong right now is my dropbox folder is not in the menu bar up top, but I'm leaving it that way and should I need to go there I'll do so as a log-in - because in the back of my head, dropbox was spazzing out, too, and he had me undo its automatic launch, and since then we've been fine.