This could be extremely beneficial to Apple's market and mind-share. Apple will see computer sales rise as people see a win-win situation and try the company's computers. In essence, they're getting two computers in one -- a Macintosh that runs Mac OS X and Windows XP. If even a quarter of new Apple customers stay on Macs, Apple's market share will boom. Developers will see this and respond accordingly.
I guess the market agreed, which is why Apple stock ended up almost $6.00 today.