Well . . . Vista, need I say more?
No, just kidding. In my opinion, they crash/freeze frequently, viruses, not very user friendly/hard to use, plus, there are a handful of companies selling essentially the same product, (all the different models kinda hurt my brain), kinda like rebadging cars.
The whole idea of sub operating systems (Home, Home Premium, Ultimate, etc.) I don't care for. Best of all, I'm a total Apple junkie.
P.*. - I truthfully and honestly don't mean to offend anyone, if so, sorry.