Aha!
I was just about to come here to post that I'm having no luck with any WiFi toggle apps. (I'm on VZW and chose not to do a factory reset -- since the absence of the toggle was the only thing that seemed to be wrong after the update.) I downloaded a WiFi toggle widget app from the play store, which works FINE for turning off WiFi, but gives me an error and stops working when I try to use it to turn on WiFi. I thought this was just the app, but had the exact same result with another app. That there thread ironass linked to confirms that someone else had this problem.
Bet it would go away if I did the damn factory reset, wouldn't it?