It looks like George Gonthier and his collaborators have finished formalizing the Odd Order Theorem.
In his earlier work on the Four Color Theorem, Gonthier invented a bunch of new algorithms (mostly variants of BDDs and graph algorithms) which were especially amenable to formal verification. Since he has said that he was continuing to use this small-scale reflection style of verification in the work on finite group theory, I wonder what new algorithmic tricks were developed during this development?