Firstly, being completely honest, I'm not satisfied with any OS I've ever run, but I dual boot win7 on my computers for games, and use Ubuntu the rest of the time. I'm a web developer/programmer, and I prefer working in the same environment (LAMP) my code is deployed on. It makes sense for me.
I love both windows and linux for different reasons, but I hate both of them for certain reasons too.
Windows 7, is by far the best windows ever. I've used them all, it's good. That said, I have had just as many stability issues as I had with XP...it's not perfect yet. On my laptop, for example, it decided to completely kill itself after an update, and nothing short of a re-install fixed it. This actually happened 2x...within 3 months. I still don't know why...but now that laptop only runs Ubuntu, cause it's too crappy for games anyway, and it's been rock solid for a year now.
On my desktop, win7 has been nothing short of a nightmare for me. I know I'm pretty much alone in this, but it's true. I would not trust win7 to important work on this machine. About 6 months after first installing win7 on it (64 bit from msdn), I got a new video card. Genuine advantage decided it was a different computer and tried locking me out. No biggie right? Just activate it. Well, that didn't work, I forget why. I re-installed. Later I got an ssd. I decided to clone my C: partition onto the ssd, as that was always easy in the past on hdds. Wrong. No matter the method I used to clone the partition onto the ssd, windows would not boot off of it (this is a fully supported intel ssd, it should have worked). Even the repair mode on the win7 disk couldn't properly find a windows installation, despite it being perfectly readable and everything (I've done this tons of times on regular hdds, with no problems). So, I ended up doing a clean install on the ssd. Everything was fine for a while. One day, win7 decided it couldn't update anymore. The error code was related to proxy settings, and trusted sites. I went through every single step in the supposed solutions to the error, but it would not be fixed. Nobody could help me out with it either. Stumped everyone that came across it. Since I only use it for gaming, it was not updated for 6 months, but then I decided enough was enough. Re-install. Currently it's working just fine...no issues. We'll see how long that lasts.
Overall, windows maintenance is the #1 reason I prefer linux for my default. On top of the hassles I've had with my desktop, I hate the way windows update works. It couldn't take any longer, and I hate that it tries to force you to reboot...it's stupid. I miss how easy it is to back up a list of software you have installed, and re-install it like in linux with repos. It takes so long to re-install software after a windows install. It's ridiculous. It takes me about 1/10th the time in linux to get everything I want installed...and I always have a LOT more installed in linux. I hate how windows handles drivers, they still, in win7 tend to mess up way too often. Viruses, I don't have problems with anymore, so I can't list that.
Linux though, I have problems with too. Every time linux's graphics stack starts getting good, fast, and stable, either xorg devs decide to break everything, or new desktop tech (compiz, kwin, gnome3, etc) breaks things with my catalyst driver. And there's the rub. Graphics in linux, across the board, is crap. You cannot find a high end card right now with a proprietary or opensource driver that is near as good as in windows. All have some missing functionality, and the opensource ones which everyone tries to recommend, perform like crap. If I were a games dev, I wouldn't make games for linux either...it's that bad. I get by just fine, cause I don't game that much, and my 4850 works fine for my uses. Applications. I wish linux had the application and game support windows had. It would sure be nice. Ubuntu in particular is terrible with regressions. I've never had an update to a new version of the distro go perfect. Not ever. Lately bugs I've personally experienced have been pretty minor, however. Wireless support could still be better. Zealots of all kinds need to go die in a fire. There's a place for proprietary, and there's a place for opensource and free...the fighting needs to stop. There's more stuff, I'm forgetting some.
So, why do I stick with linux on my desktop at all, if there is more software, better video drivers, games? Because day to day it's less of a hassle than windows is, it keeps working unless I mess with it (unlike windows in my experience), and I develop code (web stuff) that runs on linux...so it makes sense. Also, besides that, I like LVM, couldn't live without it. It makes keeping my multimedia collection organized simple as pie, because I don't have to have tons of partitions, or raid (I'll only do hardware raid, so, that's less cost not needing it). Also, I tend to find linux's desktop environments more pleasant than win7, pretty much across the board. I know I'm mostly alone on this.
Why Windows? Just games for me, don't trust it for much else, honestly...but I understand why lots of other people prefer it, and that is perfectly fine too.