The big upswing is the result probably the result of many things. I purchased my first iPod last November. Shortly followed by two Macs. I've always wanted a Mac, but they haven't always as affordable as a x86 PC. With the introduction of the Intel based Macs, my first was a Mac mini G4 at a discounted price. Within the first week, I absolutely fell in love with the OS. So, I then went out and purchased another (Intel based) for work.
Now, enter the "halo effect". I was the first in my office to own an iPod. After others seen me with mine and tested it out for themselves, three went out and purchased one of there own. As for having a Mac at work, well two others have purchased Macs since. One a Mac book and the other a mini. As the result of one initial iPod purchase, two iPods, one Mac Mini G4, one Mac Mini Core Duo, one Mac Mini Core Solo, and a Macbook have been purchased.
No different than when the PC first had it's "big bang" word of mouth and having others see the products in action (especially in a corporate IT environment) for themselves, have done accomplished something that standard advertising simply cannot.
Making the Mac more affordable, not to mention having a slick MP3 player and software, have done wonders for Apple. As long as Apple can deliver on media other than music, through iTune, and continue to innovate the iPod, they should be able to put the company into the position it should have been in the first place.
Apple Market Share to Explode?