Yes, and all over the place. However, they're not 'official' MR gatherings, just groups of people that meet up... some are more publicised than others. Some regular forum posters met up at MacWorld SF earlier this year.
There was a picnic in Regent's Park, London last year where about 30 people turned up. Someone even flew in from Norway to attend.
The people that organised last year's event are talking about this year's possible event. I believe there are also plans to have a Chicago meetup soon.