Allright.
In a game like World of Warcraft which is about epic battles and great heroes and the like, and being your average human behind most of the characters, Power RP is a widespread phenomenon.
Imo the two biggest kinds of Power RP is the one that dictates the reactions and feelings of a another player, the other is "power reactions" to other players RP.
On a small level first:
The first kind of Power RP should be more or less self-explanatory, but let me clearify anyway.
Quint: "Opathu, you look like a girl"
Opathu: *Rips Quints bony arm out of its socket*
Now as a likely outcome it may be from calling Opathu a girl, this is power rp as he takes direct control over what happens with Quints body. People get very touchy about their IC chars after a while and everything that affects them in some considerable way should not be emoted out there without the recipients agreement. Preferably let the effect of the cause be emoted by the recipient of the initial emote.
Quint: "Opathu, you look like a girl"
Opathu: *takes a hold of Quins arm and pulls forcibly*
Quint" *Quints bony arm is ripped out of its socket* "oi!"
Cause and effect thing going on here, the other player emotes the Cause, but it should be up to yourself to give the Effect. Now, giving a proper Effect to a Cause (love using silly terminology and capital letters) is hard, especially when the Effect is expected to be negative.
Which brings me to the other kind of Power RP, the denying of others RP.
Now, the balance between the giving and taking of RP interaction is a delicate one and easily overstepped one way or the other, but this just demands experience and prefereably to know the one you RP with.
RP between two persons that involves more then just empty chit chat, but also active emoting between eachother should be like pitching "ideas" to eachother, one pitches an idea/emote, the other either accepts or denies the idea, either is fine, but the more acceptance the more interesting RP.
This puts some responsibility on the pitcher as the idea he throws must be catchable. Do not throw something at a player that is impossible/very hard to accept, a.k.a Power RP. BUT, the recieving end of an emote must be able to sometimes be able to swallow his pride and accept a an emote with negative outcome to yourself by giving the proper accepting emote back. To yield in a situation might not allways be that easy, but it damn well improves the rp.
There is nothing more enjoyable RP-wise than a rp session where the flow between giving and taking, pitching and accepting flows fluently between the "actors".
I tend to play along to Power RP if it has mild exterior effects, like the other day. "elf backhands Quint making him fall into the water" This is clearly Power RP as the pitcher gives both cause and effect. But I had Quint fall in the water cause in that situation it was better for the situation as a whole to just accept it rather than to deny it as Power RP. There is no need to freak out every single time something like that happens.
But, when it comes to feelings, mental reactions and stuff that invades the sanctity of the characters personality, people tend to get really touchy.
such as,
*you feel tremendous awe and fear as you lie your eyes upon Twiglet*
This is a very often thing used in flagrsp/mrp description and its blatant Power RP. You are invading the privacy and freedom of another characters personality. How can you know how what said character has experienced in his/her lifetime? How can you possibly know how that person is put together to know how he/she will react to you? You cant.. Poeples feelings and reactions to things are their own and no one else has the right to say otherwise.
Yes yes.. mind control.. fear spells.. blah blah.. when rp'ing with these things its still up to the recipient to give the effect, though then the responsibility lays on him/her to give the proper effect to the cause, if not otherwise is agreed upon OOCly.