This is an nteresting read...

http://einstein.stanford.edu/TECH/technology1.html

The roundest thing we ever made... a gyroscope. This particular gyroscope has roundness so perfect that the only thing we know of that is more spherical is a neutron star.

There's an interesting point that says that if that gyroscope were to be scaled up to Earth size, then the tallest mountains would be 8 feet tall.

That shows both the incredible level of perfection they've achieved, and that the imperfections still exist in something so amazingly spherical.