I'm in the minority. I've had more than a few one night stands. When I'm not having regualr sex, I end up in bed with someone. It's a weakness I'm not proud of.
The only one night stand with a complete stranger was in Las Vegas. I picked him up in a casino bar. He was very well dressed and was carrying a very expensive bag. I sat down next to him and struck up a conversation, which was easy, since we were both alone. He was charming, well-educated, well-spoken, older, and he looked a little like Jeremy Irons. It was one of those "I'm in Vegas" sort of experiences. It was a bit awkward, and definitely not the best sex of my life, but it was memorable.
All the rest of them were with longtime friends or very good lontime acquaintances, men I knew for years and spent a lot of time with socially, and almost every single one of them remained my friend afterward for years. I really don't have a lot of regrets there. I chose them because I genuinely adored them, as great friends, and there was a mutual attraction, and a mutual respect.
One, actually the best one night stand of my entire life, the sex was absolutely amazing, remained a one night stand because I felt that the guy treated me disrespectfully by being indiscreet, so we never slept together again, even though I really wanted to sleep with him again and I knew that he really wanted to because he tried to seduce me again. I told him off and didn't speak to him for over a decade, he made me so mad. He recently sent me a message on Facebook apologizing for making me angry and thanking me profusely for unrelated acts of friendship that helped him that I did for him around the same time that he says probably changed his life. He thanked me for being such a great friend to him and for looking out for his best interest and expressed his regrets about how eveything ended. I still don't know if I did the right thing, but I don't react well to indiscretion from men I sleep with, which I've always interpreted as extremely disrespectful. I may have over-reacted because he message was unexpectedly warm, sincere, beautifully written, and very moving. Looking back, maybe I should have given him another chance. Who knows what would have happened?
Sleeping with a friend does permanently alter the relationship. Whatever existing sexual tension there is in the relationship increases forever, the possibility of sleeping together is greater than before. Some of my friendships suffered because of it, others seemed nearly unaffected, except the flirtation in the relationship increased. The ones I regret sleeping with are the ones who seemed unable to really be friends instead of constant potential lovers.