I think I've found a better group ride to start off with. The local chapter of the Appalachian Mountain Club, of which I am a member, has Tuesday night show-and-go rides that are specifically labeled as beginner rides that go at the pace of the slowest person (that likely being me). The distance is about the same as that shop ride. Sounds less likely to be a bad experience, and the one this week is in a town with which I am somewhat familiar. If the weather cooperates and I decide to do this one, I'll be sure to post a report!
2011 Surly LHT
1995 Trek 830