I have installed Ubuntu on the day where Windows Vista were officially anounced I'm still loving it... Windows 7 is not bad too but i like working in Linux more, i don't know why... i think its multi-desktop and compiz.
10.04 and 10.10 gets very eye candy, but i was happy with 6.06 too

Ubuntu + Windows 7.
They are very different but I love both

I hate all versions of windows with a passion. It's unstable and slow.

I mainly run Gentoo but have a Ubuntu installed alongside of it, since the VPN commection at work uses SonicWall (Piece of CR*P) and it's one of the few distros the Linux client supports.

Windows 7. Easily one of the best OS's ever. Its on my laptop and two of my desktops. If the n900 ran it I would use it exclusively.

I have Ubuntu installed on a home "server" and sometimes I'll VNC into it. I have KDE dual booted onto my laptop but I never use it.

Someday I want to get a macbook pro, but only to laugh at it and say I have mac "experience".

EDIT:

Meant to add that this summer I want to make my own linux desktop and learn each piece. Its my understanding that the kernel can be built with different "modules". So I'm going to look into learning what modules there are, what they do, and build my own kernel. Installing JUST a kernel gives you a terminal, right? Cuz I want to start barebones and install an XServer, then play around with different window managers and choose which one I like and basically build it from the ground up. I'm sure my disdain for linux will only be increased but I want to try this.

For development: I'm currently dual-booting a mac-mini with Mac OSX and Windows XP. Both systems access a Ubuntu 10.4 Virtual Machine on a USB hdd attached on it

For surfing: Using my eeepc 901 with windows xp all the time

Desktop Home: Debian Testing+KDE
Notebook: Kubuntu
Desktop Work: Kubuntu
Parents': Debian+KDE (it is easier for them and for me, because it doesn't break as often as Windoze)

Desktop: openSUSE 11.2
Laptop: Fedora 12 with encryption, mobile broadband and vmware for testing stuff
Servers: openSUSE 11.2 running mythtv
NAS: 5tb qnap nas running linux based distro
Firewall: astaro linux based distro
Work PC: Win7 (if games ran on linux I would get rid of this altogether)

Been dual booting Ubuntu and Windows XP for 4 years now. Thinking about wiping it and making it Ubuntu since I rarely boot into Windows nowadays.

OS X (10.6) on laptop, ubuntu running on virtual machine.

Windows XP on another laptop, haven't used it since I bought the macbook.

gentoo for the last few years.

Started with Linux in about 1994 with Slackware when it was installed from 6 floppies. Moved on after a few years to RedHat. When RH went commercial I moved to gentoo rather than Fedora, and never looked back.

My Eee still has Xandros but without the unionfs, however that'll be finally going to gentoo in a couple of weeks.

I run Win 2K in a VM for when I need to get compatible with a customer, but for very little else.