One of my friends wrecked doing about 50mph on a freeway interchange, and he was wearing full leathers and a full helmet too... not even trying anything aggressive, just going around a turn.
He was in a coma for 3-4 months, and still hasn't recovered full motor control and speech a year and a half later. At least his brain is still functioning normally (mostly)- he's still pursuing his master's in Mechanical Engineering.
Be careful out there.