Does time machine really back up EVERYTHING?!?

Is there anything time machine does NOT back up?

I know it backs up files and such but what about my general settings and preferences? User login and pass? iPhoto library? My iTunes?

Like...if I throw my macbook off a bridge and buy a brand new one, will a Time Machine full restore make it identical to my previous macbook?

I just want to know if I can rely on just time machine to back up everything or if I should be backing up certain things elsewhere in addition to using time machine.

Thank you!