Ironically I was just on-site for a new build out of a conference room where they wanted a USB connection in the middle of the room for a printer in the corner. It had to go under the floor and across the room, a run of ~20-25 feet, plus some slack at each end. We looked at the Active extension cables as an option but eventually decided on a different approach, mostly to not have any cable connections in the floor of the room.

We chose the Cat5 USB extender from CablesToGo. There are two pieces (device and computer) and you connect them with a Cat5 cable up to 150'. Even better for us is that the termination points come as mountable in a standard faceplate (pic in the link), so we can make it look pretty in the conference room. The kit will run you $100 for the generic dongles and about $120 for the faceplate version. Definitely more expensive, but also a much cleaner, finished look.

Also, I'm glad someone started this thread. This was the first place I came looking when the client asked me about extending the USB. Now there's an answer here next time someone needs it