This is my first big post, but I have been playing CoH religiously for the past few weeks and I have been power leveled a number of times within my super group and I haven't seen it on the forums here. Here is how it works (it may take some time to find players willing to do this, but it's definitely worth it once you do find the right people. Keep in mind this is for high level people, but can also be for low level people as well):
1) Go to Peregrine Island.
2) Ask for a farming mission group
3) If somebody invites you, make sure to tell them you're level (very important).
4) If you're within the level range of 43 to 49, tell the leader you want to be a place holder (sidekick somebody).
5) If you're lower than 43, ask one of the place holders to side kick you.
6) It is very important the leader is a level 50 fire tanker with a Dreck mission (freaks, level 50, level 51 and sometimes level 52).
It may take upwards and around thirty minutes to get a full group, but players are willing to help other players with this and for exteneded periods of time. Once the group is full and you have your side kick or are side kicked, enter the Dreck mission through the portal within the Peregrine Island building. From here on out (unless you are the fire tanker) you just have to sit towards the entrance of the mission and watch the fire tanker kill everything with their flames. The experience will roll in really fast and you have to do nothing except wait for the fire tanker to say, "reset the mission."
My super group has been doing this for the past few weeks and I believe it's going to be nerfed soon (have to be within 200m of the tanker to get experience). Get going and do this as soon as possible. This only works with level 50 fire tankers, but the good news about that is almost every level 50 player seems to have a fire tanker for this.