Well, my partner gave birth. That's about it. And I became a mother.
I didn't realise it back then, of course - being CAMAB does rob you of some things, such as the realisation that if you've got kids, you're a mom - female parents tend to be called that, regardless of whether the kids came out of their womb or someone else's.
But in the end I did realise that. I realised that other people see me as the mother of my kids, and it's ok with me. I certainly wouldn't want to be called their father; it'd be just too weird for me (it may very well be ok for you to be called a father even though you're a woman - be my guest. Just don't push it on me).
It's a right can of worms, of course; motherhood. My relationship to my mother is far from easy. She's not outwardly oppressive or anything, but she really doesn't see the kind of woman I am. I suspect she still sees me as a wee girl, a sexless child - which I most empathically am not. She just kinda ignores that. So it's not something I've wanted to imitate when raising my kids, and I hope (and feel) that I've done better by my children. They seem to be well-adjusted and decent people, and I hope it's just not my indulgent imagination. I'm quite proud of them, and I'm especially proud of the loving family we've managed to put up together, my partner, our children and I.
Happy mother's day to all of you mothers out there. And even if your own mother left a lot to be desired, hopefully you can mother yourself properly.
[ETA 18.5.2012: added clarifications]