To me, a Mac is just a Unix box. Except, unlike something like Linux:

- I never have to futz with basic configuration issues (e.g., printing just magically works).

- Software updates don't break my machine (much).

- I can install all sorts of random Unix utilities without much hassle (e.g., via Homebrew).

- I've got access to commercial software in areas where I want it (e.g., Adobe Lightroom, Creative Suite, Microsoft Office).

So long as all those things are true, I'll stick with a Mac. If, however, I can't just say something like 'brew install nmap' and have it magically work, then that's when I stop buying Macs.

Incidentally, replacing Growl with a system service for notification management is a great idea. If they want to issue some kind of oddball rule that access to this service, or to whatever else, is restricted in some fashion, I'd be curious to know how they enforce that. Will the OS kernel refuse to grant you the right to link against certain dynamic libraries? The only way I could see this being truly enforced would require a fairly draconian kernel. At that point, you don't really have a general-purpose computer any more.