Of course, Apple staff heading to Tesla isn't new. Multiple people have made that leap in the recent past, including Mac hardware engineering VP Doug Field. And the reverse is true as well: Apple has hired Tesla veterans for its own automotive work, which is significant despite Elon Musk's bid to downplay the departures. However, there's no doubt that Casebolt's exit will cut deep. Whatever you may think about the Macs he helped make, there's no question that they're clever feats of engineering. Whoever his replacement may be will have big shoes to fill, and may well change the direction of Apple hardware.