At the moment I'm using 3 different OS.
I'm using Windows XP pro for my personal use (gaming, graphic desing, and web design) and also for business use (office applications, emails, internet browsing)
I'm using Windows Vista for some of my clients most for home use. They love new graphic design and security of new Vista.
And im using Linux (suse, red hat and fedora) for my business needs like my company servers (file server, web server, database server, security gateway server, print servers, application servers)
For this 3 I realy love Windows XP over Vista. Im not a big fan of nice looking OS but the system preformance. And Vista is a bit to resource taking OS.
I also love Linux distributions becouse its stabile, secured, and free