Via Ann Friedman, Nancy Goldstein explains "why no Democratic presidential candidate is getting my gay money." I don't have any gay money, personally, but I think you've got to respect where she's coming from. It's worth observing, however, that presidential politics simply isn't a particularly effective leverage point for advancing gay rights as a general matter. If you have the chance, check out Josh Green's profile of Tim Gill a few months back in The Atlantic to see a more efficacious path.
Gill's approach, in essence, is to try to scour the country in search of low-level elected officials who stand out of the crowd for their anti-gay activism, and then get big chunks of cash sent to their opponents. Green's lead example is "Danny Carroll, the Republican [ex] speaker pro tempore of Iowa’s House of Representatives" who sponsored his state's entry into the "succession of state ballot initiatives banning gay marriage."
Over the summer, Carroll’s opponent started receiving checks from across the country—significant sums for a statehouse race, though none so large as to arouse suspicion (the gifts topped out at $1,000). Because they came from individuals and not from organizations, nothing identified the money as being “gay,” or even coordinated. Only a very astute political operative would have spotted the unusual number of out-of-state donors and pondered their interest in an obscure midwestern race. And only someone truly versed in the world of gay causes would have noticed a $1,000 contribution from Denver, Colorado, and been aware that its source, Tim Gill, is the country’s biggest gay donor, and the nexus of an aggressive new force in national politics.
Carroll lost his seat. Let that kind of thing happen a few more times over the next few cycles, and suddenly you have politicians everywhere thinking twice about whether or not they really want to be leading anti-gay demagogues. It's much easier to impact elections for state legislature, and the preponderance of gay rights issues are state-level anyway.