These are the best set of performance tools that money can't buy. Shark is the best profiler that I have ever used and blows the socks off of Metrowerks' $3000 CodeTEST product. I just got back from an Apple performance workshop where they showed us how to use their tools and they are by far the best kept secret of Mac OS X development.

Shark (the profiler) will integrate with your application's source code (assuming debugging symbols are turned on) with both Mach-o and CFM (Shark used to not work with CFM, but the latest versions do). It lets you know when you've caused the processor to stall, when you're data is not aligned, etc. and it tells you how to fix it! Apple could easily charge $1000 for these tools and they would be worth every penny. The fact that they are free is a testament to Apple's devotion to providing developers with the best tools that are available.