I've used Jamon with Aspectwerkz to do a similar job, you can find code here. I've also implemented the same functionality with
Dynaop but it more intrusive than Aspectwerkz. The benefit of Jamon is that is comes with reporting built in and exposes a web interface for the results too.
Its good to see more interesting articles on practical uses of AOP beyond security and and logging (something I'm guilty of too :)).