Randall asked this question on his blog, and I rather thought the answer I gave might be interesting here.
Chris and I always felt like we were chosen for each other, pretty much from the second time we met (the first time I was busy trying to tickle the tonsils of a girl called Sue - my only other GF). Later I can remember talking to God and asking 'how about a girlfriend?' and He would say 'go out with Chris'. I'd then disagree and want someone else: partly because we had a great friendship and partly because I was hormone-driven and wanted someone a little sexier. But I think, even at that point (we'd been BF/GF a couple of times) that we knew we were going to be married.
But it was always very clear to us that we weren't married. True, we didn't live with each other or have sex (although that was a close run thing a few times) but we KNEW we weren't married - marriage was a very specific joining at a very specific moment, and it was that moment we were working toward.
We've talked this over briefly again today. Chris's wording differed a little from mine but encapsulated EXACTLY the same idea. From the moment we made and meant the vows we were married. It was before first love-making, before sharing a flat, before cooking a meal and even before we could get away for a good kiss on the way to the reception. I'd suggest consummation *sealed/confirmed* the vows we made, but that married status was already present to be confirmed, and actually made the act capable of consummation instead of fornication if we'd not been.
So there you go - we knew from the moment we exchanged vows. I don't know if the words "I now pronounce you man and wife" make any difference. I suspect not, but for the less clued up they might be a useful guide......