These are the few user groups that I go to or keep track of regularly to see if they are discussing a topic that is of specific interest to me.
New England Java User group. It has been there almost for ever. They have some excellent speaker line up and its a very active user group. If you are new to Java or a veteran- you will always find something useful here.
Boston area Grails User Group. This is the only grails groovy user group I found in and around Boston. Haven’t attended any of their meetings yet , but seems to be fairly active group.
Boston Area Scala enthusiasts. This group was started by my friend Nermin and couple more Scala enthusiasts. They have had only couple of meetings so far- but the group is well….quite enthusiastic . At this point they do not have scheduled meetings on a particular day of a particular week. But I am sure they will get there soon. Currently, they meet once a month in Cambridge at Google office.