kaicho saidDo yourself a favor and just pass by the gay scene on Castro....
Every time I've ever been there, countless times people have been doing lines of coke or taking hits of random drugs while IN LINE to get into clubs/bars... and god knows what was going on in the shaded places.
In my opinion, that place is so far downhill that it's the Cabrini Green of gay culture. (not sure what cabrini greens are? .. google it)
Um, kaicho has been hitting the wrong places... or attracting the wrong people. I have never once been asked about drugs in the Castro. It's there for people who look for it, but kaicho's perspective on the Castro is wildly off.
Definitely check out the Castro if you have any appreciation for gay nightlife (and it's great during the day as well--lots of cute shops, bistros, and salons, and some wildly over-the-top porn shops as well). Badlands is always a safe bet any night of the week...crowded and sometimes an attractive crowd. The other places tend to be older, not attractive as often, or more "alternative" (such as 440, Moby Dick's, the Mix, and Q-bar), but being your first time you should just have fun and explore.