In the early to mid '90s I was involved in three user groups in the K.C. metro area: the Kansas City UNIX User's Group, MacCORE, and the local LUG (which, according to kclug.org, is still active). MacCORE was the largest and most organized, with dozens of people at each meeting, guest speakers, and promotional items from Apple and other companies in the Mac ecosystem. The KCUUG and KCLUG meetings were more bare-bones and less formal.

I enjoyed the social aspects of each group, but they also had a huge impact on my career. This is particularly true for the KCUUG where I served for a short time as president. One of the attendees saw me speak at a meeting (on managing an NNTP server IIRC) and asked me to do some consulting at a local ISP. They ended up hiring me, but couldn't afford a Sniffer, which led me to start writing a protocol analyzer for Solaris and Linux. That analyzer (Wireshark) now has its own active online community. We don't have any official user groups, but we do have conferences in the U.S. and Europe each year.