An Apple blog reports on a Gartner Research study of computer sales. While growth of PC sales has been an anemic 2.6%, sales of Macs over the last six months have been increasing at a rate of 30%.
My guess is that uncertainty over Vista and the potentially high cost of upgrading existing PCs or having to buy new ones is depressing PC sales. Apple appears to be benefitting from the ability to run Windows natively right along side the Mac operating system, giving users an easy migration strategy.