My wife tipped me off to this. I actually think DeGeneres (should I call her Ellen? I don't watch her show...) was really cool about this. In contrast, I believe Rosie O'Donnell was less than cool when she argued guns with Tom Selleck on her show. (Plus Selleck wasn't running for president.) What's really nice is that DeGeneres cracks a joke at the end to end McCain's misery.
I'm not really sure how I feel about the actual issue of gay marriage. In an ideal society there wouldn't be a government as we know it, and religious organizations could marry whomever they chose, while secular groups could have something analogous to getting married by a justice of the peace. Society wouldn't need to have a debate on it, just like society wouldn't have to decide whether 9-year-olds should be allowed in bars. (Of course "society" would decide in the loose sense in which society decides on the market price of a share of IBM.)
But that answer isn't really helpful for right now, and I don't really have an answer. All I can do is give my dad's favorite non-answer at a dinner party, "I feel strongly for both sides." It's like the prayer in school issue, or malodorous homeless guy in the public library issue. Both sides have very legitimate points, and with the government running things, there's no good answer.