So recently, Planet KDE has had a huge number of posts about the Windows and Mac ports of KDE and I just wanted to put in my $0.02.
I'm the primary (or at least, most public) person working on the Mac port, and I am also employed by an open-source company, and I would just like to say I agree with Aaron's sentiment. I am both a Mac supporter and an FLOSS supporter and while I can't speak for the Windows port, I can say that I have no intentions of the Mac port trying to take anything away from the community nor from open-source software as a whole.
There are large parts of the Mac community who had no idea open-source software existed for a long time, but things like Firefox (and heck, Safari's KHTML heritage) have made it much more prominent, and have driven large numbers of people to try out things like OpenOffice, Ubuntu, and KDE and see that there really is great free software out there, which is not only free as in beer, but gives you the freedom of knowing that you will always have access to it in the future without vendor lock-in, private APIs, and restrictions.
Since I first started porting KDE to Mac OS X I've seen a lot these types of arguments, and in the end, it has always appeared that everyone wins when software is available on more platforms, whether those platforms themselves are free or not. As an anecdote, when I first got KOffice ported, one of the first "thank you"s I got was from some folks who study the bible and have macs, and loved KOffice's support for bidirectional languages. Microsoft Office on mac had no support for Hebrew, and KDE made it possible for them to do their research on their own computers.
...but I digress. Ultimately I do the port because I use and like macs (as well as Linux systems), and because KDE applications have a lot to offer. I like KDE, and I wanted to be able to use it everywhere, not just when I'm on my Linux boxes. That said, it's even better if my work is useful to other people, and it grows the community as a whole. My intentions started with "scratching an itch" and if it turns out that no one uses the Mac port but me, I'm fine with that. I know that won't be the case though, there are a huge number of people who are interested in it, and hopefully they will be able to join the community and make it even better.
On the other hand, I don't know how to solve the issue of culture clash. There are certainly large parts of the Mac community who are ignorant of the Open-Source Way™ and who expect a lot for nothing. We run into those types of folks in Fink pretty regularly, and if we can, try to educate them, but it's not always possible. The most I can hope is that they don't bother the folks in the greater KDE community too much. But hey, there are also very large parts of the Mac community who are very open to the ideas of free software and if we're lucky, we can grow the community even stronger.