I am a happy Mac user and a frustrated Windows user.
I primarily use Adobe products, and between platforms, with quality hardware, they are practically synonymous. However, the process leading up to launching software, navigating and saving files, and interacting with the operating system in general is the major difference for me.
I can look at this objectively and tell you that software is software. It should not matter what platform you are on. RAM, CPU, quality parts... specs are specs.
The difference for me is the overall experience. I find Mac OSX to be much more pleasant than Windows in every aspect. I prefer Apple hardware to pretty much every manufacturer, and I prefer Mac OS to Windows. Now, I have seen some other OS that seem just as nice that have no affiliation with a hardware manufacturer, but I prefer Apple hardware.
All this being said, one of the worst computers I have ever owned was a G5 iMac. Quite possibly one of the poorest designs ever. First revision, burnt through three logic boards in as many years. The fourth board is now burnt as well and the machine is in it's box in the closet. Not even worth it's parts at this point. Poor design. Apple never admitted to the problem. This was a widespread issue with a product that should have been recalled. Apple store's response: consumer machines have a 3 year lifespan, whether failure or obsolescence. I had to work harder than I should have to have the board replaced after Apple care expired. I can understand the policy if it was out of warranty and the board failed for the first time. This was the third.
I bought a MBP last year and it is by far the nicest computer I have ever owned. I absolutely love it. I am not a blinded fanboy or whatever, but I would predict that I am an Apple user for life. Haven't purchased a PC since 1994. Work has provided those headaches for me.
My advice, from experience: do not be an early adoptee. Wait for the second or third revision of a product. The G5 iMac is a perfect example. I have friends still running their G5s after all these years. Rev. 3... design improvements. OSX 10.6... a lot of people could have held off until 10.6.2 or .3 and been much better off. I had very very minor issues, small quirks (compared to windows issues I would call them idiosyncrasies), but others reported process hangs and intermittent failures.
Software and large files seem to be so much more stable, in my experience, in a Mac environment.
Chris, Rod, anyone who knows, is 10.7 the move to true ZFS?