well.. there's a flaw in your thinking.. in your question anyway.. it's called selection bias.. tendency on the part of the sampling procendure to exclude/include a certain type of unit..
the 30 people you speak of can't be recognized as a true sample of the population... what if you were in the castro district of san fran.. where 80% of the population is gay (i think.. it's high anyway).. or what if that group of people just left a gay and lesbian rights seminar...
anyway... you see where i'm going..
you should've just asked "what percentage of the (insert region, state, country, planet - here) population is gay"