This comes from Handango: "Pocket Hack Master is an advanced utility that allows you to alter (overclock or underclock) the speed of your XScale CPU. Hack Master supprts speeds from 60 MHz to 472 MHz. Lowering the speed of your XScale CPU will add to your battery life. Or you can increase the speed if you need more power. Get detailed information on your device, system processes, threads, modules, system databases, battery and power
Apparently the 'trial' software does not adjust the speed, only shows the system information. But at US$ 9.99 a 50% speed up on certain devices would be cool.
Some tech stuff: to increase the clock of your H3970 or H5450 to 600MHz, you have to set the manual options to 27, 3, 2... According to some other info, don't change the L option too much, that controls some stuff in the LCD!
It also has a Scale option: you set thresholds for idle, low and heavy CPU loads and the software will change the clock speed accordingly. You can save power while not using it heavily, or get that "push" you need now and then. You can also check an option to always max the speed while in the cradle!