There are a number of recurring themes during Jonathan Coulton live performances.
When Jonathan plays with Paul and Storm, there is often dialog about one of the performers stealing focus while the other is performing. The classic example is when Jonathan brought a video camera on stage while he performed backup vocals to Paul and Storm's "Nugget Man."
Water is often used as a comic device during shows. This was most notable as a recurring theme at Portland, OR: 2008-04-25, as evidenced by many of the videos from that night.