If a mathematician has done his graph theory, combinatorics classes, and a special topics class or two, it's probably a good idea to snap them up. A good mathematician can sometimes turn O(n^2) performance into O(1). Of course a good mathematician can also create an algorithm that runs as a fraction of O(w) time and be happy about it as long as it proves the theorem.

Academically w.r.t maths, mathematicians start where computer scientists end. The biggest bane to graduation of a CompSci student is usually a basic combinatorics class. One guy I knew was given special dispensation to take the class after having exceeded the maximum number of fails allowed for a single class. He was to devote the entire term to just that class. He had finished everything else. Intro Biochem and Discrete Maths I were the two most failed classes.