Lee Badgett has a great, carefully constructed, analysis of the income tax consequences of gay marriage that I highly recommend.
I say carefully constructed because she essentially looks at changes in government revenue from tax receipts based on several assumptions about how large the GLBT population is and what would happen if we legalized gay marriage.
As I am doing my taxes now, the first real year in which I worked part time (at least financially -- I worked full time at two different colleges/universities, but at only one was I paid a normal salary) I am considering the implications of not being married to BioMom.
The great irony, is that I might actually qualify for the earned income tax credit (EITC) depending on if they take pre or post-403b contributed income.
I want to compare the extra earnings that I would get from this negative tax to what we were to get if BioMom and I could file jointly -- a practice that mainly benefits couples with a great disparity in their earnings.*
*Note -- I love to unravel the government's goals behind policies. This one clearly encourages the single-breadwinner model in which one person works full-time while the other stays at home. The current income tax model has quite negative consequences for couples who earn similar amounts and file jointly.