Graph Isomorphism is indeed not used much in these field. Subgraph isomorphism (and variants of it) are very useful, and surprisingly (well, suprising to me), the techniques for solving graph isomorphism and subgraph isomorphism are entirely different.<p>On practical use of graph isomorphism is finding symmetries in programs -- (basically) build an AST, and then run graph isomorphism on that.<p>Also, the algorithms used for graph isomorphism are used (with modification) to solve a large range of group theory problems, including group intersection, so this might help with a large range of other group theory problems.