Most of the members and visitors here are hikers, and the majority of the messages are about hiking. A few of us do less-common activities, so the Usergroups feature can make it easier for us to find partners. If you click on "Usergroups" in the upper right, you can browse the groups and join whichever ones appeal to you:
Routefinders: Scrambling, Snowshoeing, Geocaching
Trail Runners
Climbers: Alpine, Rock, Ice
Snowboarders & Skiers
What happens when you join a group? Nothing. It just makes it easier for other people with similar interests to contact you in the future...