Mac OS X 10.6.4, MacBook Pro, Apple Magic Trackpad.
The trackpad is unresponsive. Right-clicking on the Bluetooth icon in the menu bar shows me gray text that says "Bluetooth not available".
I don't see a system preference item in which to fight with this, but I don't see anything relevant.
Best Answer
According to this article, resetting the System Management Controller might to the trick.
Here's how to Reset the SMC on Apple's support site.