I've had to re-install machines numerous times because they became unusably slow or infested with malware. We had one machine to which this never happened, nobody really understood what made it different from all the other ones (as much as 25 machines at a time at some point), that little machine just kept chugging away. Maybe it needed an occasional reboot, but even that must have been rare because I don't recall ever having to do that. It's not like it was build with premium components either, it was mostly built from leftover bits and pieces.
I was a licensed MSDN developer for a long time, it cost a pretty penny. You've never paid license fees ? Ok, that's your decision, I always paid for the ones we used, in fact I probably paid for plenty that I didn't use (aka the microsoft tax).
For the most part though, windows was nothing but trouble for me and the people that I worked with, and since switching to linux I haven't had any experience even remotely comparable to what used to be my lot when still using windows.
The machine I'm writing this on was bought in December, the 'vista' installation that came with it was wiped and replaced with Ubuntu. It's a fair sized machine, 10G of ram and an i7 processor, this is still the first logged in session on that machine since I got it. That's amazing stability. It's possible that microsoft has comparable stuff now but I won't be seeing any of it until I either absolutely have to or they do something unthinkable today to prove that they really get it. (Such as, for instance really opening up the source to windows or some earth shattering move like that).
I'm happy you're happy with either, I'm more happy with FOSS stuff, it feels like it is a more natural and democratic approach to computing than having my capabilities granted and removed by some corporation, especially one that has been a bad little boy in the class of corporations.
this is still the first logged in session on that machine since I got it. That's amazing stability. Not sure what to say about that, I have only rebooted Windows after applying system updates for as long as I can remember but then I mostly turn it off when I know I am not going to use it for a few hours so I have never had a large uptime.
That still doesn't address the fact that this is entirely off topic as Windows OS != C#. My entire use case for C# is as the scripting language for Unity3d which is based on mono since it is cross platform capable.
Two all is comments are about Windows OS not a single one about C# which is presumably the topic at hand.