It's very rare that I go to a client and pair programming is not an issue. Developers love their desks, personal keyboard configurations, and music. I like that stuff too; unfortunately, any personal space benefits or keyboard configurations cannot make you more productive than a team of effectively pairing developers of the same skill level. I can't prove that, but you can't prove that I'm wrong either. Of course, to begin (a futile) attempt to prove which is more effective we would need to decide on what we were measuring. Building software isn't only about the number of features delivered, it's also about the quality of the software delivered. It's also about having a team that can maintain an application as (inevitable) turn over occurs.
That's what's so great about Pair Programming, it improves the quality of software while spreading knowledge and best practices at the same time. Everyone benefits from the sharing of knowledge from small things such as efficiency gaining key short cuts to large things such as understanding the big picture of the project and spreading common patterns throughout the system.
Adopting pair programming isn't as hard as you might think. In May of 2005 I wrote that setup is important. I was wrong, setup is not important, it's the most important step towards adoption. Anyone looking to bring pair programming into their organization doesn't need to do much. Get tables large enough for several team members to sit in the same area comfortably. Get the latest and greatest desktops for the pairing area. (My current client got me a beautiful Mac Pro). Get a desktop with dual video out if possible, or get a video splitter. Buy 2 keyboards, 2 mice, and 2 (large) monitors for each pairing station. If the pairing stations are the best systems to work on, developers will naturally migrate to those machines.
70% of ensuring adoption success is work station set up.
I suggest not mandating pairing, let it happen naturally. I also suggest allowing the developers to keep their desks. Everyone needs an area to escape to and read slashdot when they need a break. If you just bought everyone 30 inch monitors you may need to move those to the pairing stations and give everyone small monitors for their personal desks. The idea is to allow people to have their space, but encourage them to use the pairing stations by providing a superior set up.
20% of ensuring adoption is ping pong pair programming.
Ping pong pair programming is fantastic at keeping everyone involved and given the opportunity to drive.
The remaining 10% will vary by organization, but if you handle the first 90% the rest should just fall into place.