In order to use a power on someone, you have to do it via /vp command. Lately I have been hearing from some people that they have used it, but I haven't seen the message or that they're afraid that they'll get MGed.
Well, if you want to use a power, you have to do it over /vp, otherwise it is considered as powergaming. The other party has to see your /vp message. Failure to do so will result in ajail.