Guys, you should stop using Black Sludge unless you REALLY know what you are doing.
I mean, what stops it from being tricked back to you, crippling not 1, but two mons?
Ontopic, as Lee said, Nidoqueen has the wonderfull ability of countering specific and dangerous threats. When placed in a well built stall team (like one i saw once, but i dont remember who was using it) it can be pretty effective, even though her weaknesses became more proeminent this gen. I just wish she could use Slack Off (4 moveslot syndrome would become more evident, but it would also give her the much needed ability to switch back and forth)