I remember learning an amazing randomized algorithm for max cut. If you pick edges at random 50/50 to be cut, you get a 2-approximation to the optimal solution. That is it's no more than twice as bad.
The first approximation algorithm, invented by Erdős. The best known by Goemans and Williamson achieves about 0.868 (IIRC) approximation, and is a thing of beauty as well.
Really not bad for "just guess".