I'd never heard of P.A. Semi until I read a headline this morning that Apple had purchased them for $278M. Interestingly enough, this buyout of a semiconductor company which makes power-efficient embedded computing chips has met with positive reaction on Apple's stock price. While it's likely that these new chips will be destined for Apple's lineup of portable devices, usually news of a purchase has a reaction on Wall Street in the downward direction as cash is depleted.
Apple is also due to make an earnings report after the bell today, which may be pushing the stock higher. Apple's continuing success with the iPhone following price cuts internationally may also be responsible for this movement, as well as optimism about the upcoming 3G iPhone.
