Bluetooth Not Available? 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.
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.