Apple's stock has plunged over 10% in after hours trading since Apple announced record and expectation beating 3rd Quarter results, currently sitting at just under $150 after closing at $166.49.
Apple's stock price is notoriously volatile after quarterly conference calls due in part to Apple's habit of understating estimates for future quarters which they routinely beat. In addition to a low forecast, Apple's gross margin was lower than the year ago's quarter.