I'm continually amazed by the asymptotic complexity of union-find, which is O(alpha(n)), where alpha(x) is the inverse of the Ackermann function (and n the number of sets you union). In other words, O(6) or so as long as your inputs fit into the observable universe.
There's definitely a divide on who sees what sort of algorithms. The subject of this article is in Graph Theory space, which a lot of us get even without trying (I dabbled in TSP for a while because it's a difficult distributed programming problem and I wanted to explore the space for that reason).
But if you're not implementing AI or game engines, some of the linear algebra space may be a road less traveled.