Ususally no. I might mention an incedent that was offensive (and change details, names, etc) if its in context to the topic but I've found that too much negativity or snarkiness is not good for my blogging karma, you know? Its just not always that constructive - IMHO. I'll never say I wouldn't ever do it but will avoid it if I can. Anyway, too many ppl I know read my blog so, even if I reeeeally wanted to (shoot I have SO much to say about my mother!) - I couldn't without getting myself into trouble! :)
I would, if I had already made it clear to that person that I didn't like them or I was unhappy with their behaviour. I try not to talk behind someone's back in real life, so I wouldn't do it in a blog either.
Well, I've never gone off on someone on my blog. I try to keep things light and fun. Complaining about a rude receptionist or a slow waiter is one thing but I just don't think my readers would find my personal tiffs interesting.