[uahal]

Seems to me that if a person is leaving a company for a different opportunity, they're making a clear comment on their perceived future value of the company.

That is, who would leave Google in 2002? Dell in 1993? Facebook in 2006?

In my opinion, the best stock exercises are cashless, one time events, paying full short term capital gains. Those trades represent almost no risk to the exerciser (exercisor?) and are pure financial upside.