According to Apple Insider, US Federal District Judge Kenneth Karas has issued an order preventing Mark Papermaster from taking his new position as a vice president at Apple, pending a decision over IBM's "no compete clause" inspired lawsuit.

Apple and Papermaster have responded, but Daring Fireball doesn't think they have much to worry about, give "Application Group, Inc. v. Hunter Group, Inc., 61 Cal.App.4th 881 (1998), a California non-compete clause case":

We further conclude, in agreement with the trial court, that California law may be applied to determine the enforceability of a covenant not to compete, in an employment agreement between an employee who is not a resident of California and an employer whose business is based outside of California, when a California-based employer seeks to recruit or hire the nonresident for employment in California.

Basically, California don't play no-compete, and Papermaster's going to be employed in California, so IBM's legal maneuvering, while time consuming, is probably not a deal breaker.