As promised, here are a few of the local IT groups that I rely on for insight and incitement. They all have maillists, so you can participate even if you aren't really "local".
National Information Security Group, at naisg.org
NAISG is a great group with a diverse membership- from students and teachers to law enforcement personnel, systems and network administrators, consultants and security entrepreneurs. The mail list is a good resource for technical information, but the real value of the list is often the insight into the "why" rather than just the "how". Join the maillist here.
[Full Disclosure- I have been an active member since shortly after NAISG's founding, I serve on the Board of Directors and I am Chairman of the New England Chapter]
The following are not security-centric, but are very good groups:
Southern New England Network Users Group, at snenug.org
A fantastic resource for small to mid-sized business admins. Often MS focused, but a wide variety of topics come up. One of the best remaining resources for small business Novell gurus.
Boston Linux Unix Users Group, blu.org
From beginners to experts; Unix, BSDs and Linux; this is the place for *nix information and insight.
Boston Area Windows Server Users Group, windowsboston.com
One of the largest Microsoft user groups, Windows Boston is also an affiliate of the Boston Exchange Server UG. All things Microsoft, and more.
[Full Disclosure- I'm an advisor to the Steering Committee]