I use a Linux distro full time (Fedora to be exact) as the host OS on all of my machines. I do have Windows machines virtualized however...
I'm blown away by the sheer amount of ignorance in this thread though. I don't really mean that in a negative way, just in that I'm amazed at how little even some folks who read a "technical" site such as this know about Linux. Also, I'm amazed how how many people have either half-heartedly tried it (without really trying) and dismissed it as a 'toy', or believe many myths and haven't even tried to try.
I'm not going to be petty and point out anything or any one in particular, but for those of you who haven't tried a Linux distro in a long time (more recently than say the last 3 years), download an Ubuntu, openSUSE or Fedora LiveCD and try it out...you might be surprised at how easy it has become.
Ubuntu will work the "best" out of the box for the average user, since they are based overseas, they have more liberty as to what they can include by default in their distributions as they have no US Patent encumberments. Fedora for example is backed by Red Hat, and is based in the US (North Carolina), and because of those restrictions can't ship the distro with certain codecs installed by default. As a result, the distro is more "free" and has nothing proprietary built in. However, it's very simple to add the RPM Fusion repository and gain access to all you need...Ubuntu does make it simpler for a "first time" user, or even someone who just "wants it to work".
I like Fedora because it's really cutting edge...the Fedora project does a great job of taking the latest packages and somehow making them stable, and as a result they are usually a "release ahead" of Ubuntu, at the slight risk of some instability...I'm experienced enough to deal with it, and adds some spice ;-)
Also, I'm not a distro "fanboy" - I don't care what distro you use, but hey, give something a shot. I use Fedora, but Ubuntu is easier to get set up, and Linux Mint looks very nice as well, is based off of Ubuntu and has even more "non-free" stuff installed by default making it even EASIER to get going
P.S. As for the guy who said he would switch when a large, major corporation switched all of their desktops (not their servers) to Linux, last time I checked, Google was pretty major and they run a mix of Windows, MacOS, Fedora and Ubuntu. Red Hat is pretty major too, and all of their desktops run Red Hat Linux Enterprise. Also the entire City of Key Largo Florida runs Novell Suse Linux Enterprise, Shuttle Computers uses Foresight Linux on their internal computers (As well as offering it for sale on the kPC)...these are just a few examples.