Paul Murphy has a story: Pssst... Free Linux! Only $799!. Note that the point he's making isn't against Linux, or even Red Hat - it's against suppliers of hardware and software that essentially force you into paying for an expensive Red Hat license that you don't want.
The nub of it is:
If your application vendor only supports one of the Red Hat enterprise editions and this obligates you to pay at least $799 for your first year, is it still free?
Of course not, and remember - it's not Red Hat's fault. It's the other vendor adding a bad dependency that is the problem.
We have a system bought to run a particular piece of commercial software. This software used to run on SGI boxes running IRIX. And any old SGI would do. But our O2s were getting a bit long in the tooth and not really up to it, so they offered to let us transfer the license to Linux. Which is where the trouble began. The vendor's spec for the machine didn't put it in the bargain basement category, and we had to get a Red Hat Workstation License - not cheap - and a fancy quadro card - not cheap either.
Even worse is that we had to use Workstation 2.1. The application just refused to work - point blank - under 3.0. (What is it with Linux compatibility between releases? Don't the distribution builders or application suppliers care? I have applications running flawlessly under Solaris that are 15, 20 years old. God I love Solaris.)
Which is another common point - many commercial applications seem to want a Linux version that is, to put it nicely, antique. Red Hat 7.2 is pretty common. I don't understand why this is. Is it that it doesn't work under newer releases (often, yes, unfortunately)? Can't they be bothered to get it working under something newer (who knows)?
(This phenomenon isn't restricted to Linux. We've had the same problem in the past with commercial applications under Solaris not supporting current versions. Or even Sun stupidly not supporting their own hardware under current Solaris [think back to the disaster of the Sun Blade 1500 and Solaris 9 - ours sat in their boxes for 6 months because Sun couldn't be bothered to get Solaris 9 running on them - and that after delivering them months late]; or Sun not supporting their own products on Solaris 10 yet [or Solaris x86] - think SunRay.)
Overall, this is the biggest beef I have with commercial application software. Not it's quality, or price, or anything religious about licensing. Simply the fact that they force you into a straitjacket when it comes to configuring your system, and that hurts.