I used this approach when taking pics at a friends wedding in Cornwall, UK a couple months ago. I stuck close to the pro photographer but kept a reasonable distance at all times. We chatted and discussed kit and his experience although he wasn't a native english speaker.
I had no place taking pics in the church during the service and let him do his thing with his fast primes as no flash was allowed.
During the styles couple shots etc. I stood close to him and quickly took pics of the same scene. I also allowed him to shoot first so my flash didn't annoy him too much.
When things got a little more relaxed later on, he asked me to take pics of him with friends (he was also a friend of the bridal couple) and he did the same for me.
When I ran out of memory and battery, he continued to shoot great slow-sync shots on the dance floor which I was envious of
The lessons I learned:
- be aware of your behaviour around a pro/designated photographer who has the pressure of recording the big day
- shoot in JPG instead of raw so I don't run out of memory
With DSLR's becoming more and more popular, pro photographers seem to have to tolerate guests and enthusiasts taking pics of the same scene.