the interview proc for the big ones is intense. you might fail the first time... often times they will TELL you what you failed about. usually you can fix that.Maybe someone in here can tell me if this is true... But for Google internships my friend was telling me how they had about 4 rounds. You have to solve a problem, and it has to hit some Big O value. If it's slower than that, you're OUT. Disqualified.
You really really have to know your stuff in these technical interviews I suppose lol.