I'll admit that there are a bunch of neat features in Mustang (and even in Tiger) that I didn't know about...
JeanFrançois describes how he used two features in
to locate a
difficult memory leak.
He is converted, but do check the comment thread.
There is more information on JHat through several blogs:
Mandy's entry on
From Monitoring to Diagnosing Memory Problems in Mustang.