One of my core beliefs is that it's easier to keep a group going if you keep the overhead low and stick to a formula. I spend perhaps 45 minutes a week on http://www.opass.org business, and probably an extra hour the week of meetings to get things ready, and I count on volunteers to help out with the running of the meeting (sign in, order pizza, clean up, etc), but not as much in between meetings.

Steve, I think you're on the money about people rotating in and out of groups. It's normal and everyone should understand that!

The time commitment part I think relates to perceived value. Our group (www.opass.org) meets bi monthly. We did this originally to reduce the stress of finding speakers, but it turns out our members love it because it does reduce their time commitment without making them feel guilty about skipping meetings!

There's huge value in having a chance to sit in a room with people from the same profession but different employers and just talk. Not everyone sees that, and not all groups do a good job of fostering it, but it can easily be as valuable as whatever technical topic is presented. If user groups work at providing value - think of themselves as a mini business - I think they can survive and even thrive.