I did a group shoot of about 100-120 people for a company's yearly conference about a month ago. I had about 10 mins. to coordinate and get the image.
I used a tall ladder and was able to find a slightly sloping hill to have everyone stand. I used as small aperature as possible. It helped to have a assistant from the group who knew everyone and could take my ideas and get people on a personal basis to do what I asked. I took about 10 images total, not to bracket, but to be sure that averyone looked OK (all eyes open, looking he right way, etc.). Humor goes a long way as well...
Good luck!
