Concerns about "Gay Marriage"

During my morning rant at the television embodying Howard Dean on Russert's program, my wife raised a question that stopped me cold.

"If gays can marry, what would keep two women living as roommates after college, for example, from deciding to 'marry' for benefits? One may have a job in big corporate America and the other employed by a four-person business. Now big corporate America would end up with another medical bill. Doesn't this seem like a huge invitation for fraud? How do you assure that the two women are lesbians or not?"

All I would add is that the biggest case of marriage for benefit and government observation is immigration. And we all know that the INS has terribly efficient at identifying marriage fraud in that case, right?