Less lumpy than a billiard ball. The mountains and trenches only seem significant because the whole thing is so big. Totally not a perfect sphere though, yeah.
The myth is springs from the fact that if you had a smooth earth with a radius of center to Mariana Trench, and another smooth earth with a radius of center to Mt. Everest, you could shrink both of them by the same factor and fall within allowed billiard ball specifications. That says nothing about smoothness, only about the allowed size of ball.
If you actually shrunk the earth we're living on, the ball would still be rejected as quite too rough.
If you shrunk the earth down to the size of a billiard ball and the imperfections where only as rough as the bumps in medium sandpaper then that's still pretty darn round even if it wouldn't be acceptable under official billiard ball specifications. I never could get behind the idea that it would be smooth as a billiard ball but to know you could feel the ridges is pretty neat and yet it's very very round.
