If it's part of a broad-based stock market decline, not much. The risk of plummeting equity grants to Bay Area tech companies is that your employees will go to the company next door whose equity is going up like a rocket. If everybody's miserable and poor, then they just go on inventing stuff and coming out with new software.

Honestly, I think the Valley is much more fun to be in during busts than booms. All the folks who just want to get rich quick leave, and you're left with the people who actually make things.