It's rare to see a good application to test out the performances of your Mac. HighLoad seems to get the job done.
You control all the tests from one simple, two tabbed interface divided in tests and utilities. Your Mac's performances are shown as load average and Mach factor at the top of the interface. What I liked about this application is that you can perform all the major troubleshooting tasks quickly: set to CPU maximum, launch the graphics visualizer, image rotate and test available memory. HighLoad can also allow you to quickly disable specific features like sleep and screen saver, to get a better testing environment. The time spent testing will be indicated at the top of the interface.
Apart from these operations you can launch the Terminal and create a disk image and even perform more common tasks like purging cache, verifying preference files and rebuilding the index in Spotlight and Mail.
In all, HighLoad is very handy to test the general and specific performances of your Mac and see if something is going wrong. The simple interface makes it accessible to anyone. Recommended.