I've shot two friends' weddings myself. I'm reasonably happy with what I was able to accomplish, but the pro I hired for my own wedding outclassed anything I could have done, both in terms of the gear he brought and the effort he invested. He set up big studio strobes with radio remotes and strategically hid A-frame step ladders around the place, allowing him to get up over the crowd and shoot down at people. As others have mentioned, he was ubiquitous yet unobtrusive. His main line of work turns out to be doing "executive portraits" (i.e., those shots you see of corporate executives in the airline magazines) but he used to be a newspaper photojournalist.