Apple has been doing its homework, at least since Steve Jobs took over as iCEO, before the turn of the century.
The result of all that effort has been a mix of eye-catching end user features and lower level enhancements that are apparent only to developers and benchmarkers. Apple has already made it plain that the next major revision of Mac OS X, Snow Leopard, will concentrate on the latter.
Stating "The Mac is poised for innovation over the next few years on a scale that we haven’t experienced since the initial move to OS X in the previous decade," Cult of Mac makes the point that the iPod and iPhone are already with us, and will require only maintenance design and engineering henceforth, freeing valuable resources to return to work on Apple's main product line, the Mac.
Perhaps, but even when most distracted, Apple managed to incorporate KPIs and DTrace into Mac OS X, as well as flashier developments like Core Animation, laying the groundwork for future advances. Snow Leopard will take that groundwork much further, with Grand Central and OpenCL.
One upshot is that Apple will be in a far better position than Microsoft to take advantage of multicore (2, 4, 8, ...) processor architectures, hyperthreading, and GPGPUs, as they become available, dramatically increasing the performance advantage that Mac OS X has already established through successive optimizations, while Microsoft has continued to rely on faster hardware to take up its slack (a practice that is now deeply engrained in Microsoft's corporate culture).
One result is likely to be that many companies will find the combination of an Xserve and a dozen Mac minis significantly more cost effective than the Windows PCs they replace, even before taking into account that the Xserve comes with Mac OS X Server which includes serious, easy-to-use groupware, making it simple to set up various collaborative modes.
Another likely result is that the average consumer will finally come to view Windows as being something you only buy if you can't afford better, a situation which, realistically, has existed at least since Mac OS X 10.4.3 was released, and which has become painfully obvious with the release of Mac OS X 10.5.4.
Of course, as with many supposed bargains, the total cost of ownership for a Windows PC is typically higher than for a comparable Mac. For now Microsoft can rest easy in the knowledge that this point is lost on many consumers and will probably remain so for some time to come.