Don't judge all windows machines based on the bad ones. Remember that Windows based computers encompasses everything from very very low end to extremely high end and powerful (better than any MAC on the market). The issue is most companies and people go inexpensive and low end giving the OS the bad rep when in reality it is the low end product that should get the bad rep.
It has nothing to do with the hardware, its the OS itself. I've been using various computers (Unix / Win 3.x to Vista / Mac OS / OS X / Linux). The unfortunate thing is that the Windows OSes (especially those with network access) tend to get bogged down after time. I've repeatable had to reinstall the Windows OSes from scratch to get the machines functioning properly again.
Where this hasn't been a problem is when I keep the Windows OSes in a VM, and don't use them to access much internet. Install very few programs, and things stay stable.
Comparing that to my current Linux or OS X systems that have gone through multiple OS upgrades on the same hardware. I've never had to reinstall the OS from scratch, they just keep working great.