OK so I'm late to the party... I hate to stirr up the thread again but I had to respond
In line with the OP windows has come far with virus prevention. With the latest and greatest windows, good virus protection and firewall software and not have a moron for a user... windows is pretty stout.
As far as "real world" applications for Linux based OS, that has come a long way too. Think about it... Apple is using PC hardware and running their OSX software. PCs aren't ONLY running windows anymore. You have hybrid systems that run OSX with boot camp running windows.
For me I'm stuck. In the medical field you have to deal with software interface. Hooking the medical device to a computer to calibrate it requires you to meet the specifications listed in the user manual. You can be legally liable if a calibration is done on a computer running emulated software. It sucks. It really sucks. It means I get to have an old, slow ass computer cause I need a serial port that meets IS&T virus protection and firewall requirements while the computer itself is an old ass P4 with 512Mb of ram running Windows XP.
The only game I play on a computer is Guild Wars. The MMORPG is still massive... many many people still join up on World of Warcraft and Guild Wars. Neither game is compatible with other OS. Emulating the software on OSX or Linux would probably work but not very well as it takes quite a bit of resources to run the game.
I haven't been fond of mac but I hate iTunes with a passion... trouble trouble trouble...