Wow, a lot of people seem to consider it to be "a quick fuck and then forget about it".
I'm a bit weird and different. Simply put, I never had much support from my parents and I've never had an official relationship. With the result that my friends are very important to me. Still being too paranoid to do one-night-stands (being transsexual puts me at the risk of everything), I'm kind of out of the ordinary game so to speak.
Being poly I tend to be a little attracted to several of my friends. All of them are ok with it and do not mind the occasional cuddle, even if they have their own reasons to not being interested in the naughtier stuff. Sometimes I wonder if my friendships are equivalent to other peoples relationships. An actual girl/boyfriend would be different in that they would be the person that I would want to form a family with. And hopefully doing kinkier stuff with.
All that said, I consider my best friend to be on the same level as an boyfriend. He has been the substitute for a partner all these years. I want to sleep with him, but I have no intentions to get in the way of his love life or relationships.
TLDR: Friends are important to me, sometimes there is a bit of attraction and I wouldn't mind sleeping with them. I honestly do not see how a bit of attraction or sex gets in the way of a friendship. To me it means that I'm comfortable with them and trust them (and that they are in my taste).