Although they're great - danlmarmot was insured courtesy of Netscape for a year or two - what really sucks is that same sex domestic partner (SSDP) benefits are taxable according to the IRS. Because you can't marry, you can't satisfy their requirement that only benefits for your family [i.e. your spouse and children] are tax-exempt.
As a result, you wind up paying upwards of a thousand dollars a year in additional federal income tax as a result, which sucks.
On a vaguely related note, one thing that has always pissed me off about the whole gay marriage debate is the total lack of any sort of empirical evidence or rational thought. I could almost stomach conservatives arguing that gay marriage is a bad idea because we really need the income taxes we get from taxing SSDP benefits, even if that seems patently ridiculous because most gay couples would likely pay more taxes if they married [assuming roughly equal salaries, filing as married would seem to throw you in a higher tax bracket overall]... it's just this vague "uh, if they marry, then my own marriage will somehow be less sancred in the eyes of God" bullshit that irritates me.
'Specially when I think of Britney Spears in Las Vegas.