Oh, I now just realised there were three questions in the TS, my bad.
So what operating systems do you use? - As I said before, I'm a user of almost every OS.
These OSs are the ones I've used in my life, not counting any Virtual Machines, Live CDs, nor Customer PCs.
Linux: Debian 1.1 all the way to Debian 7, Ubuntu 8.04 LTS to 12.10, CentOS 5.x and 6.x, Arch Linux, and Linux Mint 5 and 6.
Mac: Anything from 10.6 to 10.9.
Windows: WXP, WVista, W7, W8, W8.1.
Android: Anything since 2.1, only had Nexus Phones and ASUS Transformer Prime tf201.
iOS: 3.x and 4.x.
Windows Phone: 8.
Symbian: I don't remember, I had that Phone for 2 days only.
Are you thinking of upgrading to a different one? - Always when a new Version is available to the Public (or to Developers, if it's OS X), I get it right away, without any thinking.
In my opinion, Windows XP was the worst Desktop OS I worked with.
I mean:
1. Driver Installation was a pain in the arse, and it becomes only harder and harder.
2. Viruses easily enter Windows XP from every possible corner.
3. Weak Multi Tasking.
4. No .doc, .xls, nor .ptt support out-of-the-box.
5. Improper File Manager Navigation.
6. Limited Customisation without the need of any 3rd Party Tools.
7. No choice in Window Managers nor Desktop Environments; you're stuck with what Microsoft gives to you.
8. It's impossible to switch to a different language than the one you installed it in.
9. You can't control the entire OS by Command Line.
10. Weak Permission System; everyone is Admin, when exploited correctly.
And do any of you use a linux distro? - Yes, I used Linux for the first time in the (early) 90s, just after my father let me practice on his MS-DOS PC. Debian was the Distro I used first, and I was fascinated by the ability to use a Desktop, have a Mouse, have multiple stuff running at the same time, etc.
