When I started brewing this fall, my second season (I don't brew in June, July, and August), I, too became a member of the 1.020 club. My first season, I brewed a dozen MW extract kits, all different- ales, porters, wheats, and they all attenuated right down to the specified FG in a week or so (I always use the Wyeast Activator packs). To my surprise, when I started brewing in September with MW kits, two of the first three batches got stuck (or became very slow) around 1.020. The wheat batch fermented out very cleanly in a week, but the batch of porter and a batch of ale both got stuck. I made the mistake of racking the porter anyway, and it's been sitting in the secondary for three weeks, with a bubble maybe every minute, not changing SG much, despite the fact that I agitate the carboy often. The ale I left in the primary for an additional week, and it reached the upper end of the specified FG range (1.014), so I racked it. I've decided that what I've got left in the porter is basically unfermentable, so I'm going to bottle it along with the ale this week.
After reviewing my methods, the one thing I was doing last season that I forgot to start up again was the "drop of olive oil" adjunct to æration. I've started doing that again.
Interesting times....you learn more when things don't go as expected.