I'm Windows based (Win XP x64) running with 8Gb of RAM with no problems. I can't see me ever switching to a Mac - purely based on the amount of software which I have installed - it would probably cost me around 5x the cost of the machine to switch. Plus I would have to keep an up to date Wintel system as some of the software which I run is simply not available on a Mac.
Having said that, I do spec and build my own systems - if I had to rely on buying from Dell et al, I would probably switch tomorrow. Both platforms are capable of being pretty mean machines - but for a Wintel system you probably need more detailed knowledge of components etc.
Well I'm qualified to comment on these items. I recently switched to Mac and so far am pretty happy. Parallels works wonderful for those items that you can't live without and there's no substitute. But you know what? That particular list of software was whittled down when I realized a lot of them were utilities that covered some weakness in the Windows UI or infrastructure - code bondo if you will. The list was further whittled down as I plan on keeping my MacBook Pro targeted for photography - no games, no fluff (I did say it was a plan - Garageband is tempting me to have some serious noisy fun! ;-). So the Windows software I run on Parallels will be such to maintain this focus.
I have also found the Mac world has a few bones in the closet covered by dirty laundry. It seems there are an awful lot of scripts - and utilities to schedule these scripts - to maintain the mac. Now some people say they're necessary, some people say they're not. I guess I'll wait and see on that one.
One of the most impressive things to me is the Mac sleep mode. It wakes up in a jiffy and apparently sips so little power that the case gets ice cold and has no measurable effect on battery life - which by the way I routinely get 3 or more hours out of it.
I finally gave up on x64 with my systems simply because I was unwilling to buy replacement hardware that had stable drivers. Speaking of which, motherboard and chipset drivers have ALWAYS been problematical for Windows systems. In all fairness to Microsoft most of the things folks bash it for are not their fault - rather the manufacturers of the various sound cards, video cards, printer drivers etc etc do a crappy job as they just want to get it on the shelves as quickly as possible. These are the things that make Windows unstable at times and it is difficult to impossible to track down where the issues are coming from.
Anyway - I still have both systems but I'm really digging the new Mac and marveling at it's smoothness. Will I move over completely? I doubt it. Will I prefer one over the other? I'm leaning over to the Mac for more and more but I'll defer judgments until the honeymoon is over and the Mac turns on me. '-)