The groups can be beneficial for support (ABC for example), and the others can be great to get to know attendings/mentors which can help you find research opportunities, preceptors, or simply learn more about the various specialties. The vast majority of the groups do not require mandatory meeting attendence, assignments, ect, so are a very low commitment, but offer lots of options that you can participate in if you wish. It's a different story, of course, if you decide to be part of the leadership of the groups. Here's what I've experienced...
I joined the Surgical Society during my first year. They have a few good workshops that were fun such as surgical knot tying, a hands-on laparascopic workshop, a workshop for identifying surgical instruments, and a preceptor for a day program to follow surgery attendings or residents. The attending I was paired with allowed me to scrub-in and assist on a 6-hour abdominal surgery the first day. I ended up choosing him as my preceptor, and doing my MSA project with him. I've now got two publications pending and more on the way, a trip to Carmel to present my research, with lots of great surgery experience along the way.
I joined the Emergency Medicine Interest Group (EMIG) during my MSI orientation and was on the steering committee for my MSII year. They are by far one of the most active student groups on campus. Suture clinics, intubation/chest tube/thoracotomy clinics using cadavers, IV/blood draw clinics, EKG night, hands-on ultrasound workshops, etc. Regardless of what specialty you ultimately go into, the workshops are great experiences. You get to know the attendings really well and have contacts to use later.
Lastly, I joined the All 'Bout Couples (ABC) group my first year and was on the steering committee 2nd year and beyond. My wife enjoys the fellowship with the other med school spouses. They meet often and can lean on each other when things get tough. Most of the really active members have kiddos, but we're really trying to expand the activities to better accommodate the significant others without kids.
Your last question about maintaining a marriage is difficult to answer. The overarching suggestion is to keep it a priority. I know that sounds trite, but there's just so much that goes into it (regardless of medical school for that matter). We will send out an announcement that there will be a spouse/significant-other orientation while you guys are at your orientation retreat (or right before so that the couples can attend together). We'll try to address the real concerns of the rigorous training in as uplifting of a manner as possible.
Okay, I've procrastinated from studying long enough, back to it...
