It all depends on what you wnat to do. I use both Windows (and prefer XP to Windows 7 - my XP was also more reliable than 7 - unfortunately, H/W failure cost more to fix than to buy a new, very cheap Desktop (4GB, AMD64 and 1TB HDD) that came with Win. 7. I used Ubuntu on one lap-top and both XP and Ubuntu on another. I also use Zorin_OS (Ubuntu-based 11.04) in VirtualBox on my Win. 7 system - Zorin_OS, BTW, provides 3 Desktops - Gnome 2, Win. XP and Win. 7. I also used DOSBox on Win. 7 and the Linux systems (the "old" DOS stuff runs well in XP). I also use the DOS Emulator and WINE (XP based) with the Linux systems. So very darn little that runs on Windows won't run on the Linux installs. Of course, if you want to spend the money, you can buy a commercial product (supposedly more robust than WINE), you can probably run everything,.

It is ironic that if you have Windows 7 Premium (or less) that you have to install a VM to run XP. Gee, I can do the same thing on Linux too (and from what I have read, it runs faster than it does in the corresponding VM on Win. 7. Now I wonder what will happen when Windows 8 hits the market? To get an idea, check out the Ubuntu switch to Unity from Gnome 2 (started in Version 11.04).
One reason why I am switching to Zorin _OS Core 5.2.