Err yes - just having a cuppa and contemplating what a good idea buying one was as it was the first ride wearing it! Came off when the front tucked in on an off camber wet road, with new tyres and a smattering of diesel. Luckily nothing serious (about 20 mph), the bike is not too badly damaged and I've walked away with some bruising but that's it.
However I can confirm the following:
1. I don't remember the vest inflating - it just was even before I hit the ground.
2. It was fairly tight once inflated but not ridiculously so and I took it off fairly quickly as soon as I realised that everything still worked.
3. I was using it without the inbuilt back protector as was using one in my jacket.
4. It didn't noticably restrict getting my helmet off but to be honest, I took it off fairly quickly.
I don't fancy trying that again but will put that down to one of my better buys.