Yes, you should go to a Meet Up!

Never been to a Meet Up because no business gets done there? 
Here are three reasons you should go & two why you should not. 

Preface:
Meet Ups are the physical manifestation of the Internet's skill at "ridiculously easy group formation"[1]   The barrier to creating one is low and the membership is self selected. The organizer is deeply invested, has expertise and enthusiasm. On the other hand, attendees have at least a passing interest in the subject, and the unscheduled time to attend.
This is not the formula for high quality business networking, but you should go anyway.

Three Reasons to Attend a Meet Up

1. Learn something new. Since most of the people attending are probably dilettantes, be one too. Find a speaker, a technology or an idea about which you are curious and get exposed to it. It is cheaper than a TED talk and much more fun than an online webinar.
2. Uncover a new perspective. Meet Ups draw a diverse crowd. There will be students and many who are not in your field. Embrace the opportunity to explaining what you do, why you do it and how it matters to someone new. You will learn from it.
3. Rediscover what you know. If you are an expert in the subject, a Meet Up is revisiting your Freshman classes. You may not learn anything new, but you will have a chance to revisit the fundamentals from which you can refresh your approach to the problem. 

Two Reasons Not to Go

1. Job Interviewing. If the only reason you are going is to find a job, don't. (For career fairs - try Greenhorn Connect) Yes, there will be someone at a Meet Up with opportunities, but they aren't there to interview you. Meet Ups are a great opportunity to discover new companies. Absolutely follow up, get the interview, get the job, but don't attend 'looking for a job'  Everyone is tired of that conversation.
2. Making a Sale. It is rare to find someone with dedicated budget and decision making authority at a Meet Up. If they had budget, they would have the vendors come to them on company time. You will meet the influencers and hear the inside stories of why certain technologies or services are or are not being chosen. Meet Ups can provide good intelligence, but this isn't selling.  

No two Meet Ups are organized the same way, so choose a couple to try. Whatever subjects you choose, you need to participate. Be ready to ask the first question and start random conversations. Who knows where it might take you. 

Footnotes
[1] Seb Paquet's original blog from 2002
[2] My links to Clay Shirky