To be totally correct on the gay thing; during the pre-donation interview, they will ask you, if you are a man, if you have had sex with another man, and you will be disqualified if so (or, at least, I presume it's very likely). If you are a lesbian or a gay man who has not been sexually active with another man, you're good; on the other hand, if you consider yourself straight but you've had sex with another man before (hey, I won't judge), you're out. (At least as far as California goes; I'm not sure to what degree this may vary by state or country.)
Yes, it's misguided and not fair, but please don't let that discourage you from giving blood if you're eligible. Someone who's having a very bad day and needs your blood to survive shouldn't have to suffer because of some unrelated bureaucracy's misguided policy.