For our December meeting we decided to have several groups, each with a different topic, a la Open Spaces.
http://www.meetup.com/NYC-GTUG/events/39017292/
There were two overwhelming themes in the comments we received:
Pro: Members felt more comfortable asking questions in a smaller group, and felt that overall they learned more.
Con: There were too many interesting subjects and they were reticent to wander between groups since they were afraid that they would miss something. (I was leading a group, but really wanted to attend the talk on regular expressions.)
Overall, this format was quite successful and we will try variations on it in future meetings to see what format works best for what type of subjects.
I was personally and particularly pleased, since each group leader was a member of the GTUG who stepped up to share knowledge with their fellow members.