I think this has been asked at least 1000000 times on the forums. Lol. Never gets old though, but no, that's not something my partner and I are interested in engaging in. We're strictly and happily monogamous, and neither of us have interest in anyone of the opposite sex.
Sex is way to intimate/private and special for me to allow someone besides my partner to watch. If I'm naked, and especially in the act, I find that very special (I guess would be the word) and it's not at all something I would ever want to share with another person. I just couldn't "give" my body out like that. I don't mind changing clothes in front of family members or friends who are female, but I'd never let another male see me naked. Ever. I'm sure my partner will be the last male to see me naked, no matter what happens.