The classic argument against Linux as desktop is that it's a pain in the ass to set up, and once you have it set up, none of your programs work anyway.
My last couple of Linux installs disproved the second half of that theory. Between OpenOffice.org, Mozilla products, and a lot of hard work by the open source community, pretty much all of the day to day stuff is covered and covered well. In my last Fedora install on my office computer, I even got a few different versions of IE running so that I could do browser compatibility testing.
Some parts of Linux still require tweaking to set up properly, but I'm here to tell you that my new desktop environment was worth every minute.
Sabayon Linux is not very well known, but it is at the very forefront of interface design. It is the official distribution of the Beryl project, which officially rocks. Mac users may notice some familiar behaviors - a thing that works like Expose, genie in a bottle minimization, etc. Beryl running on KDE is basically the best ideas from Macs, PCs (almost all the keyboard commands are familiar to PC users), X-Windows, and some new tricks combined into one interface. It's evolutionary from a state of the art point of view, but revolutionary if you consider that the best desktop environment out there is now coming from neither Redmond or Cupertino.
In honor of the hard work of the Beryl developers (and to show off a little), I made a video showing some of the visual effects. You can watch it here. Notice the hexagonal desktop (you're not limited to the four desktops that a cube gives you), the jiggly windows, transparent terminals, fold out effects, and (my personal favorite) windows bursting into flames when you close them.
From an ease of use point of view, it's worth noting that after I shot that video, I plugged my camera into my computer, which auto-detected it, copied the AVI file over, converted it to FLV format, and uploaded it. The process took about ten minutes, and half of that was figuring out whether I had a video conversion utility.