Apart from the weight, I think that the Canon EF 70-200mm f2.8 lens would have been ideal for this shoot, but, hey, I haven't yet found the funds to buy one of those... However, the longest lens that I do own (a Canon 135mm f2.0) was the ideal prime lens to use given the size of the venue. It meant that I could shoot people from far enough away to not be too intrusive, but still get tight enough shots.
And that's really important to me. I have been to a few seminars where a photographer has been in the way and causing a distraction, sometimes even getting in between the participants and the instructor (that really annoys me!). I inevitably lost some shots by not being more bullish, but I'm comfortable with that. People attend these events to learn something and have fun. Having some decent photos as a record of the day is nice, but it's not the reason for being there.
Overall, I think it was a success. I got some decent shots, I learnt more about shooting action in (changing) low light conditions, and people seem happy with the results.