There's Pro/Engineer, Maya, Softimage XSI, Houdini, Photorealistic Renderman, Mental Ray, and Amazon Paint in the modeling/graphics/rendering department, IBM DB/2 and Oracle in databases, AMBER, Gaussian, and dozens of others in computational chemistry, Mathematica, Maple, and Matlab in mathematics... The only areas I'd say where linux lacks high-end apps are video and sound editing. But maybe I'm forgetting some categories.
It does lack many popular applications, of course. The one that bugs me most is Photoshop, because the Gimp just isn't as UI consistent/fast and I can't afford Amazon Paint.
I find day to day use of Linux to be very nice. Installing new software/hardware can be a real PITA, depending on the exact circumstances.
OS X is nice but runs on somewhat overpriced hardware.
Windows 2000 is pretty nice and runs on inexpensive hardware.
XP is Windows 2000 as imagined by Big Brother and color-schemed by Big Brother's 4 year old sister.
Linux can be a pain to configure but is very nice to use day to day... and it's free (not that most people I know pay for commercial software anyway).
So linux is my fave but I'd recommend a new iMac with OS X or a midrange PC with Win 2K almost anyone apart from those who'd like to learn a new environment for its own sake.