I was hunting in RS (as my paladin of course) and got mezzed.... (we had 2-3 mobs in camp at the time, and no mezzer, so things were already a little hairy). Not only did the mobs all ignore me, but it seemed there was even some memwipe after mez wore off - I was the last person up, and I was able to sit down, mem res, and get enough time for it to ungrey and me to start casting it on the cleric's corpse before they jumped me - was kind of odd (and handy) that they were ignoring me that long, even seated.
Oh yeah and something i like to do when fighting where mobs mez is to get some of the jester's poisoned bread, the tiny little dot on it should break mez for you. I used some after the incident described above and it seemed to work (though I didn't get a special message or anything); at least I was never stunned/mezed for long after that.