yellowrose from my experience Top/Bottom is more a discription of the relationship between the two players then it is of the general lifestyle, with its roots in the world of gay S&M. An example in todays terms is if I go to an event and another person approaches and asks if I will "Top" them, they are asking to particapate in a scene where our relationship begins and ends with the scene. While there are people who's main practice is mainly limited to encounters at bars, clubs and events, most of that has faded with the sad demise of the Gay S&M bars.

You might want to check out the thread Tour Guide started on this.

Hope that makes some sense.