Here are a couple more celebrity sketches done in a theme park to keep limber and attract guests to the retail location. These were completed in 2006 and 2007, both at Sea World... but on different coasts of the United States. These definitely took a bit longer to complete than the average theme park caricature - perhaps 30 minutes or more.
I forgot to mention that the materials used for this style of drawing are the Dixon Markette marker and Prismacolor Art Stixx for color. You can see more work like this, as well as the process, in the book Rejects..