I do not know what the current salary/options numbers are but is it really high-reward for the top notch engineers they are seeking at this point in the game?
However, it is known for engineers working on successful teams and products to obtain additional grants that can lead to them leaving Google with several $million worth of stock.
I'm not sure if slewis's 'absolutely' answer is based on something like the latter - in which case you have to make sure you are working on high-value projects that are going somewhere.
But you are competing against 'top-notch' (to quote op of this thread) engineers for those types of awards. You'll also sometimes hear complaints about politics in the promotion process. It seemed mostly fair to me based on the promotions of engineers whose work I was familiar with.
My impression is that it's no so much "encouraged" as required. "Publish or perish" (academia), "up or out" (military), and "20% time" (Google) are all roughly equivalent. Roughly.