I was asked to take some pics at a family wedding 3 years ago, although they hired a "pro" (quotes deliberate) for the main shots. It was a learning experience I strongly recommend using flash at the reception - I tried to do 3200-6400 or higher ISO shots (on Delta 3200 and Tri-X) with no flash to not ruin the mood, but that largely didn't work out (lighting was turned down extremely low - I tried metering it, it came out to 3-4 EV generally). Also, it was an open bar and the guests were very well lubricated and couldn't have cared less about flash at that point