In the NH area there are bunch of folks interested in arduino. No official regularly meeting exclusively about arduino that I know of, but there are (3-4?) hackerspaces and quite a few folks in the gnhlug (linux user group) interested in arduino.
Hackerspaces
Port City Makerspace (Portsmouth) -http://www.portcitymakerspace.com/
Seacoast Makers (dover)- http://www.seacoastmakers.com/ ( I didn't know about bout this one till I was looking for the portsmouth address seems like they just meet-up)
Tekarts (milford) - http://tekarts.com/
Makeit Labs (Nashua)- http://makeitlabs.com/
Greater NH Linux User Groups- AKA: GNHLUG - WebHome < Www < GNHLUG (if you sign up for the mailing list its low traffic and you'll be able to get a hold of when meetings are)
ManchLUG - Manchester @ The Farm Restaurant normally last Tuesday of the month
DLSLUG (Hanover)- In one of the Dartmouth collage buildings, first Tuesday of the month i think. recently a someone did a talk on the rasberry pi!
If there are enough folks interested I'll consider organizing a monthly meet-up here in Manchester, topic being open source hardware not just arduino