Cascade Bike Club breaks their rides into the follow categories:
Easy: Under 10 mph
Leisurely: 10-12 mph
Steady: 12-14 mph
Moderate: 14-16 mph
Brisk: 16-18 mph

Strenuous: 18-21 mph
Super Strenuous: 22+ mph
There are currently only 5 different events for Easy rides under 20 miles in length, so I can see how it's daunting to someone just getting started, and looking for a group "no drop" ride. There's more than twice that number of Strenuous and Super Strenuous rides.
I'm not a fan of group rides. I don't do pacelines, I don't like riding in a pack. Sometimes I like to stop and take pictures, or sit at a park bench for a few minutes and just enjoy the afternoon. On Sunday I did 30 "Steady" miles by myself while doing errands. 14mph average, but I also stopped at a park in Bellevue and did some people watching for a while, and I
stopped at the mall in Redmond to pick up some See's chocolates for The Girl.I saw quite a few well practiced groups when I rode STP last month. They were all very awesome looking, one right after the other, wheel to wheel, well coordinated in their movements, and flying past me at 20+ mph. I overheard one group talking at the Centralia stop:
"We should back it down a little bit to 23."
"Maybe. It's getting a little hot for the 25-26 we're keeping right now, I guess."
Yeeeeah. That's just a little bit out of my league.