Apple ported DTrace to MacOS some time ago. This is very good for everyone. However one would be surprised if wanted to instrument iTunes (and perhaps more applications) - you can't by default as they changed dtrace code so you can't measure some applications.
From Adam's post:
"Which started me thinking... did they? Surely not. They wouldn't disable DTrace for certain applications. [...] But that's exactly what Apple's done with their DTrace implementation."