I use Windows - mostly for two reasons:

• The family likes the familiarity of the apps and the user interface. I've had Linux in the house before and nobody would even look at it. I didn't ask them why since it meant I had a PC to myself :-).
  
  
• I've typically bought PCs with proprietary stuff on the motherboard (like Dell, Gateway, etc) because they're often cheaper. Linux can be tricky with those - I fought will an ACER motherboard for a long time to run a Mandrake distro and when the hard drive died, I just gave up on the whole thing.

But, the things I hate about Windows are:

• Most apps try to talk to the internet frequently. I'm never sure what they're doing. I may think I know but without some sort of network tool (which doesn't come with home versions of Windows that I am aware of) I'm never sure what those apps are doing when they access the 'net.
  
• The apps that are truly useful are expensive. The ones that are not expensive are maybe useful but often limited in capability.
  
• So many apps are so *huge*! For example, I wish I could find an mp3 player that didn't try to do everything imaginable - just play mp3s without sucking up a ton of resources.
  

Lately I've been trying to populate the Windows box with some good Open Source apps and I've been quite happy with those: Mozilla, Gimp, etc.