I just made the jump from Mac to a custom built Windows box at work. It's a ton of effort to get things moved over and set up again, but my god is it fast and stable and reliable and FAST!
Cost my company a fraction of what it'd have cost to get a new-old Mac, and they were all stunned that I asked for a Windows box. Strangely, I feel more productive and less stressed now.
I can say that Windows ain't your grand-dads OS anymore.
Further, I think the iPad and iPhone will continue to be the platforms that Apple focuses on. The iPad is not really a replacement for a desktop for most of us here, but it's good for what it is and it keeps you in the Apple ecosystem.
To everyone else considering the jump, my advice: Get your trucks elsewhere if you can. Mobile computing is where Apple is going.