Reading you guys' stories is enough to make me realize I got off lucky. I get along with my MIL pretty well. She's actually way less annoying than my own mom. And what I do find occasionally annoying is pretty much the same stuff my husband does. So at least we're on the same page there. That's what's important.
The only thing I could imagine worse than having a nightmarish in-law would be also having a spouse who thinks that person can do no wrong.