I can't remember it was me or Tom who came up with the idea to use them to build a garden bench. It turned out to be a really simple structure and very easy to make. Here's a picture of the completed bench.
The only tricky part was how to get the seat to stay on it without sliding off. Here's how we did it
The seat basically consistes of 2 boards nailed to cross pieces made of 2X4s cut just short enough that they fit down into the openings in the pipes. Once the seat is fitted onto the pipes, it creates a surprisingly sturdy bench. And, it is easy to move around.