Can A Woman Have A Male Friend Without Sleeping With Him and Vice Versa

I personally believe that a woman can have a male friend without sex involved and vice-versa but a lot of people argue against this and say that it is impossible. They say that eventually they will end up sleeping with each other whether they like it or not.

What's your opinion? Have you ever found your self in a situation where you slept with your friend or best friend of the opposite sex? How did you feel afterwards...guilty or did you want a repeat?