Recently I was asked, what is it that developers get out of belonging to a User Group? I listed three things. First is the opportunity to interact with other people with a similar set of interests and skills. Software development is an inherently solitary profession, but smart people (and pretty much all the software developers I've met fall into this category) like to both learn from and impart knowledge to others. Another way of saying this is that developers are vain and boastful and love showing off their stuff. However, it's no fun showing off your latest creation to people who only understand one word in every three you say. Either way, user groups are a great platform for this.
Secondly, user groups provide excellent technical training, often covering topics that a developer may not have considered exploring on his or her own. Many developers have told me of an "ah-ha!" moment they've had when some obscure connection between the presentation they've been sitting in and a project they've been working on suddenly becomes apparent. User groups are an ideal forum for this cross-pollination.
Finally (and somewhat related to the previous point), user groups provide a platform for professional networking. Being seen as an expert in a particular field, either by presenting on that topic or by answering questions on it at a user group, can be a great introduction next time someone is looking for such an expert.
Do you belong to a User Group? If so, have I included the reasons you go along? If not, why not?