The biggest problem is the GDI. The entire graphics architecture is very poor. This is not helped by the fact that NVIDIA and AMD driver teams pour 99% effort into Windows drivers and we know how dependent on drivers graphics cards are. On Linux distros at least there are open source drivers. On Mac, you have to deal with flaky drivers with missing features, instability and poor performance and you can go months and months without driver updates and basic showstopping bugs remaining unfixed. And when the update does come, it does so at the expense of crippling performance or other bugs, which again takes few months more to fix.... It is really painful. And let me not even get to the fact that the fastest graphics card available for a Mac Pro is Quadro 4000 (of course the Mac edition costs more than the non-Mac one...), which is quite slow. Oh, and there are just two PCI-e slots without using an expander! While Windows or Linux machines can race ahead with Quadro 6000 or GTX 580 which are 2-3 times faster respectively and can use many of them. Then comes other limitations with the GDI such as it is restricted to 8-bit, while today's cameras shoot upto 16-bit, etc. etc. etc. I could go on and on and on. Of course, Windows has the absolute killer feature - Direct3D. That's the whole deal with Apple - they don't care about what you want - they will only give you what they want. If you are lucky enough to subscribe to their beliefs, good for you! Unlike other companies which look out to cater for customers, meet their demands - and suffer for it with much lower margins and less rigid integration. What this also means that for the few usage scenarios they had in mind, Apple products will work great. If you want to do something else, it's not pretty. Here's a simple example - my professional work is based around CUDA (Premiere Pro, Davinci Resolve - can't do without CUDA). Try buying a Macbook with NVIDIA.
