The idea of using slack resources — in the form of time, technology, and support — to bolster employee innovation falls in and out of favor. The return on slack innovation programs can be prodigious: 3M Co. attributes the development of the Post-it Note to its 1948 decision to allow employees to devote 15% of their paid time to side projects; and Google says its “20% rule,” which upped the ante on slack time devoted to innovation, yielded Gmail, AdSense, and Google Earth. But few, if any companies, have stuck with time off for innovation and other slack-based programs for as long as 3M. Even Google has reportedly waxed and waned in its commitment to its 20% rule.