This forum seems a ton more serious than any other forum I visit. Most of them are filled with routine jokes and smiles and happiness while this one is pretty much all business all the time.
Is that because the mod staff keeps everything on topic or because fantasy baseball players have no sense of humor?
Us mods for the most part just try to keep the boards from de-evolving into chat and flame forums. The threads seem more serious because there are some of the most intelligent fantasy players I've ever seen who post here. I actually think there is a pretty good balance of humor mixed in with the information.
As far as running jokes go, there are tons of them that have been going for several years. Most people catch on to them fairly quickly even if they weren't around for the origins. Some of the more popular running jokes that you will often see references to are Matt Riley, 3 HR Games, Cole Hamels is God, and the Texas Rangers.