The two meetups I attended this semester brought together programmer types, but could be seen as vastly different in terms of purpose and scope. The first meetup was a GirlvDevelop It Coffee and Code event, which brought together women working in programming careers or those learning to program. The other was Triangle Open Data Day, which was an all-day event that attracted people involved in open data in all sorts of capacities. You can read about my experiences here and here.
The Girl Develop It Coffee and Code felt like a support group of sorts for female programmers. It was primarily a social event where discussions were open-ended and not directed toward any one topic. On the other hand, Triangle Open Data day had the specific goals of advocating for open data, teaching tools for working with open data, and working on hacking projects dealing with open data. In my opinion, the latter was far more interesing and useful to me. I'm generally not the type of person who seeks out peer groups for career (or any type of) support, so I probably will not attend meetups that don't have actionable goals like producing code at a hack-a-thon or gaining knowledge at a professional conference. It's not to say that groups like Girl Develop It aren't beneficial to some people. It's just not my cup of tea.
Overall, I will definitely continue to keep my feelers out for meetups. If nothing else, they are a good venue for networking and meeting some pretty cool people.