I have both windows and Mac systems. They are so similar to each other now, it's almost irrelevant what would be easier or better. It's just a matter of taste. The one thing which Mac has with OS X lion now that is a useful professional tool over Windows is the new mail client. It's brilliant, as I could connect to an Exchange server account in a snap. Also, the out of the box apps are quality. Ical rules. However the Mac version of Office sucks. But no problem, just install Windows boot camp and run office 2010 VIA virtuals. But apart from that, I still prefer Windows for various fine tuned networking things.
If Macs became the enterprise standard, my new saying would be, 'Would you like fries with that?'
I think you might be right that Microsoft will continue to dominate the corporate environment, at least in the near future. That's largely due, IMO, to the large investment in existing applications. The pace at which Mac devices are being adopted in the consumer space supports the argument that there's nothing really driving Windows' dominance anymore other than price -- PCs are still cheaper. Applications are plentiful for non-Windows platforms these days, which wasn't the case in prior decades.
I think there are two ways that the current PC dominance could change rather dramatically: 1) more applications transition to Web interfaces built around HTML standards (i.e. not Active X or some other proprietary implementation), 2) BYOD (bring your own device) making inroads into large shops.
In the case of the first scenario, where applications transition from thick client to browser, more apps can and likely will transition to Web interfaces, displacing the need for a Windows-only solution at the desktop. Any industry-compliant browser running on any platform will suffice. But that won't be the case for all applications. In a corporate environment, there will continue to be legacy Windows-based applications. Terminal emulation software exists for both Windows and Mac, so the workhorse mainframe platforms aren't an issue.
In the case of the second scenario, where employees choose their own computing platform, this could change corporate environments dramatically in a hurry (within three years). Many corporations are looking at ways to reduce costs and provide more flexibility when it comes to computing platforms. From an information security standpoint, they're also looking for ways to limit information leakage. To these ends, hosted virtual desktops that remain securely within the datacenter achieve all these goals. They allow for a Windows platform to host legacy applications virtually, via thin clients on Macs, iPads or other tablet devices (i.e. whatever the consumer chooses), and they prevent data leakage if the device is stolen (data remains in the datacenter). In this scenario, it's Intel, HP and Dell that would be most directly affected, as Windows licenses would still be needed for the virtual environment. Think about the administrative implications... no multitudes of hardware configurations to manage, just a virtual platform and the applications to configure.