Rarely had a noobtube attached...
It's almost not even worth it. I'll attach it to get an achievement or when I'm really low level and don't have anything else unlocked, but that little bit you use it, the entire lobby is whining about you being a tube whore.
When I tried to get that mortar assignment done on BF3, all I needed was 2 kills but it took forever. I think you have to put it directly in someone's pocket. I'd just sit in a corner and lob them. Got called plenty of things for that.