BMC did his 90 minute engedu talk on DTrace at google to show some of its coolness (and from the looks of things to help get a Linux port going). DTrace looks awesome for system instrumentation (like strace on steroids)(although limiting it like that does it no justice at all). From the DTrace Page: “DTrace is a comprehensive dynamic tracing framework for the Solaris Operating Environment. DTrace provides a powerful infrastructure to permit administrators, developers, and service personnel to concisely answer arbitrary questions about the behavior of the operating system and user programs.”
Its the #1 thing that has me all excited about leopard (shipping with dtrace by default) and i genuinely cant wait (maybe now ill spend the extra minutes finding out how growlNotify manages to occasionally hose my box ;> )

The video shows off the Python UStack helper, but i also seem to recall seeing an piece on how dtrace can be used to debug and trouble shoot javascript and ajax (which is uber!)
Anyway, check it out.. it was designed originally (i think) to help sun engineers observe whats going on their customers machines (at every level from the app down to the kernel), and with a genesis like that its future for hax0ring looks awesome..

SensePost’ers can grab a local copy of the video [here] the rest of you have to [get it] yourselves