Although a seemingly small group, there are a couple of significant groups that I've been to that are worth mentioning.
My first experience was with the West Michigan .Net User's Group (http://www.grdotnet.org/). The turn-out was impressive, but the presentation and affiliation with Microsoft personnel was more than impressive. This group is well worth your time if you live near or in the Grand Rapids, MI area.
Next in the Lansing .Net User's Group (http://portal.artemis-solutions.com/glugnet/). Generally the meetings are on the MSU campus, and the turn-out is incredible. Here, I thought .Net developers were scarce - until I went to one of these meetings. Wow...
If you have .Net groups in your area that meet regularly, please feel free to leave feedback, posting information - or at least a link to their site so other developers can find them.