Another big factor for the communities' explosion was their misuse. The way communities were displayed in your profile page leaked enough metadata that people started using them as badges instead. Some time around 2006 people started creating communities with nonsense names, and it was not unusual to see people with hundreds of them on their profile. Things like "I cry everytime I see Mufasa die" or "Nobody expects the spanish inquisition" were the kinds of titles used in order to display your sense of humor.

In some sense this is akin to Tumblr's hashtags we see today, in which people abused the metadata channel to convey real meaning.