What is it ?
MUG stands for Magnolia User Group. A Magnolia User Group ... can be a lot of things. In general, we'll refer to MUG when talking about a local and self-organized group of individuals who meet on a semi-regular basis to share their experience of Magnolia.
MUG meetings are organized by and for users. Magnolia, the company, will happily help promote or setup an event, and team members might visit the MUG meetings, depending on localization and availability. Skyping in is also always possible.
Most user groups are accronymized to xUG (JUG, ...) It's only natural ours would be called MUGs, and provides for a good excuse to provide some fun swag.
The Amsterdam MUG used a mosquito for their logo: http://translate.google.com/#en|nl|mosquito