Over at Roughly Drafted Magazine, Daniel Dilger has an excellent article on why
Apple is set to overtake Microsoft in the desktop market. It is interesting to read how Microsoft is basically repeating the very same mistakes Apple made back late 80's and early 90's: no innovation, high prices, and writing off competition as not being a threat. As I have written in my
previous posts about OS X, Apple has a viable (and actually better) competitor to Microsoft's Vista.
Daniel mentions that Apple may overtake the middle to upper tier market, with Windows machines (and their makers: Dell, HP, Gateway, etc) fighting for the lower-tier-deep-discount machines. You know, the ones filled with all sorts of pop-ups and trial-ware begging you to buy the full versions?

And for which you must pay an additional $200 to $300 for a decent warranty. If that becomes the case, you'll have pretty much three markets: 1) the low-tier Windows market, 2) the mid-to-upper tier Mac market, and 3) the Linux dominated (in my opinion) server market.
IBM was once seen as unstoppable and un-topple-able too...but arrogance and marketing mistakes changed that. I will be watching to see if Microsoft wakes up and changes their business plan before that happens.