It sounds like joke made on April 1st. But it seems to became reality. However Apple's intentions behind the acquisition are yet far from being obvious. Hence there is room for speculation:
Top candidate seem to be a next generation iPhone. Apple might follow the plan to get the basic hardware for it under their control. However, the specs of the Pwrficient (all those LAN-Interfaces) seem to contradict.
Another option might be that Apple plans to release a series of smaller more spcialised devices like the Applte TV, iPod or even the iPhone. Apple might to intend to built them upon a common hardware platform based on P.A.Semis know how.
Since Mac OS X is already a multiplatform OS (x86, AMD64, PPC and ARM) a switch like this is not a big deal for Apple. On the other hand P.A.Semis offerings (the Pwrficient first of all) seem to deliver a better performance per Watt than even the most recent and future Intel offerings. Otherwise P.A.Semi won't even be an option for Apple. But as Steven Jobs said: We like to have options.
Apple is always good to surprise its commnity!