At the D8 Conference, Apple CEO Steve Jobs indicated we’re heading into a post-PC era.  But Steve Ballmer, Microsoft's CEO, sees more growth for PCs. Is the era of the PC really waning? WSJ's Nick Wingfield joins Simon Constable on Digits, along with guest host Eric Savitz of Barron's. And, mobile apps may be all the rage, but they could pose a serious threat to your private data, WSJ's Spencer Ante reports.