It's the same as pretty much any big company - underperformers are notified that they're underperforming, put on a performance improvement plan to help improve their performance, and if they still don't improve, they're fired.<p>There're no quotas for removing people (good riddance, the "fire the bottom 10%" school of management always struck me as the best way to create a poisonous, stressful company culture).  But it's usually blatantly obvious who the underperformers are...they're the folks who haven't accomplished anything over the last 6 months...