I stop at almost all stop signs. If it's a very familiar intersection, in a quiet area, I'll unclip and slow and look, and go, but other than that, I stop. I ride on a lot of country roads that are narrow and winding, with a suburban population. In other words, there's more cars than planned for these kinds of roads. Even though there's so many cyclists around here that drivers are somewhat used to us, I don't trust anyone.
As for the group rides, the 2 groups I ride with once in awhile are very safety conscious. But, I see other groups blow through signs on a regular basis. I worry more about the squirrelly riders who don't signal when they are slowing.