A former co-worker of mine went to work at Pivotal Labs, where full time pairing is the mandate.  After just a month, he quit "the best company he'd ever worked for," and wrote up a lengthy blog post on why pairing didn't work for him: <a href="http://mwilden.blogspot.com/2009/11/why-i-dont-like-pair-programming-and.html" rel="nofollow">http://mwilden.blogspot.com/2009/11/why-i-dont-like-pair-pro...</a>