I would perform a sexual activity to please my partner, but only if I am getting something out of it as well. There is no point doing it unless 'both' parties are enjoying it.
My wife and I have been swinging for a while. I came across this site via a google search and it seems like a fun place to hang out and meet like minded individuals.
My wife and I have been swinging for 10 years now, on and off. We have experience with MFMF, FMF, full swap (same room and separate) and house swap. We haven't ventured into the MFM scenario yet, but I'm sure it will happen sooner or later.