Mob testing stories?

Where I work they haven’t really got into pair programming/testing, and mobbing is something that almost no-one else has heard of.

One of the product themed teams has started to try pairing, but are hesitant about trying out mobbing.

I’ve read various articles and books online (inc the one by Maaret Pyhäjärvi and Llewellyn Falco), however I’m curious what experiences my fellow Club members have had?
I’d like to hear stories of where it hasn’t gone well, or started badly but improved, as finding positives is easy, whereas if I look like I’m only showing good examples they might think I’m not being objective with it.

Then who knows, I can persuade people to come together and try mobbing a piece of work and show it is about getting the best out of everyone, not the most out of them.