That fat tire bike is a Surly Pugsley. I know a guy who has one as his only bike. He rides over a thousand miles a month, year round, and fast. The bike is heavy and those tires are massive but I've seen him maintain over 20mph in a pace line for over 40 miles on that thing. He rarely does road rides but he comes along once in a while. His tires are slicks because he literally rode the knobs off if them and he's probably over 60 years old. Tough dude.
When I met this guy on a ride, I thought he was a young kid until he took off his helmet at a rest area. My friend said he joined the group for a 100 mile ride and kept up for nearly 80 miles, on a nearly 40 lb Pugsley! Until I saw it, I did not believe it was possible. The next day, one of my friends went out and bought one for wjnter and bad weather riding. Cool bike!