My husband and I were swingers first, and still swing on occasion. One of the guys I am dating is interested in trying it out with me, as well, and the other swings with his primary partner. My girlfriend is unsure how she feels towards it, and it quite honestly may spell the end of our relationship.
I think it's exhilarating. Sometimes just going out and completely letting go (okay, not completely since I still have rules/boundaries) is exactly what I crave. Watching my partner with someone else is very exciting to me.