I switched in 2002, just after Jaguar came out. One of the main benefits of OS X, in my opinion, is that it doesn't crap out every 6-12 months like a Windows install. I always found my self needing to reformat the HD periodically under XP, to get things running correctly. I've had several Macs, including this 4.5 year old PowerBook and just never felt the need to do 'fresh installs'. I always upgrade when installing a new OS version, and things seem to run fine. And with new Macs, I just use migration assistant to import the old accounts. I'm don't install lots of apps or hacks. My main reason for not wanting to reinstall is having to dig around boxes in my garage for some of my software license keys, as well as software that I bought as downloads (e.g. toast). Who know where those serials are now.. Also, I like my settings as they are, so reconfiguring would have to be a pain too.