I think there's only one person that I know of who has removed me from their facebook/msn, and that was because he's pathetic and we got too serious apparently and he isnt the "relationship kinda guy" so instead of telling me straight he wussed out and rid of all contact! I am slightly bitter, as you can tell. But I got him back in my own way.
On msn I have my talk to's and don't talk to's, it's very rare I prune. I've never pruned on facebook.