The survey conducted by Michael et al. (_Sex in America: a definitive survey_) shows that on average American has about two or so sex partners in a life time. I am quoting from memory (my copy of the book grew legs and walked from my office) so I might be off a bit, but the number reported was shockingly low. The survey was conducted on a representative sample as opposed to convenience samples most other sex studies were conducted. The main finding of the survey that sex life in America was much more mundane and pedestrian than commonly thought. It did not surprise me at all - sexually hyperactive groups are a tiny minority; most people marry the guy/gal next door who is their only sex partner (especially for women).
Wojtek