I use Win7+Ubuntu Maverick or Lucid. I'm generally staying away from Ubuntu Natty (the newest one), though. (They changed the interface on me and I'm pissed, shouldn't be a problem for new users)
Ubuntu is a flavor of linux, for the uninitiated.
It really depends what you spend most doing on the compu-
[Casual User] If you spend most of the time using the web, on facebook, on geeksaresexy.net, or chatting with friends, your choice of OS really doesn't matter. As long as Firefox and Chrome run on linux, that's mostly all you need. However, I find Ubuntu a lot shinier/glossier/simpler and a lot more responsive with a billion windows open. Also- you might rekindle your love for IRC chatting!
[Gamer] If you spend all your time playing lots of games on the compu, then go with Windows. Most big studios write games ON Windows FOR Windows. That having been said, there a lots of games for linux, and Wine lets you emulate lots of Windows programs though the emulation is often randomly glitchy, and many (if not most) simply don't run at all. I run Steam on Ubuntu, but my flashlight in Half-Life 2 doesn't work- stuff like that. Some people run their games from linux by using VirtualBox to run windows in a virtual machine. I just reboot- takes me like 10 seconds. It's not like I'm gonna run any other program while I'm playing a game..
[Graphic Artist] Photoshop and 3D Studio Max CAN be run on linux, but, as with games, they're randomly glitchy. I'd rather use Windows for them. However, the new Blender interface is really good, and it's built to run on linux. Also, I think Maya runs natively on linux. Not to start a flame war, but I personally don't like GiMP as much as I like Photoshop. A lot of people swear by it, however.
[Coder] Nothing on Windows comes anywhere CLOSE to the linux toolchain for coding in almost any language (except Visual Basic and derivatives). It's all free and very powerful. Most code written standards-compliantly also compiles on Windows, so I just write all my code on linux and compile any final code on Windows. Installing any program/lib/SDK you need is literally as simple at typing 'sudo apt-get install awesome-program'. It'll download and install for you while you nuke some nachos.
I find I like *using my computer* from the window decorations, to my glossy 3d taskbar, to my spinning cube desktops A LOT more on linux, though I dual-boot a lot for occasional Photoshop or 3DSMax use and double-checking Word docs.. Linux can do A LOT of awesome stuff that Windows can't- ask me here for details. Also important, if you're talking about an older computer, linux will make it run MUCH MUCH better than newer versions of Windows. Come to think of it- the older your computer is, the more you should install linux on it.
As WebShaman said- Try dual booting, you can try for a while and then make a choice. Install Windows first, and setting it up in the Ubuntu install is a breeze.
Good Luck! Let us know what happened!
(Edited by Petskull on 06-13-2011 11:20)