Turns out, the PowerPC G3 chips that powered Macs for years are still powering hardware, albeit in space:
The RAD750 is a radiation-hardened single board computer manufactured by BAE Systems Electronics, Intelligence & Support. The successor of the RAD6000, the RAD750 is for use in high radiation environments experienced on board satellites and spacecraft. The RAD750 was released in 2001, with the first units launched into space in 2005.
As Thomas Brand points out, the RAD750 can be found in all sorts of cool missions include the Deep Impact comet chaser, Mars Reconnaissance Orbiter, Kepler space telescope and Mars Curiosity rover.
I bet my Clamshell iBook would do okay in space. That thing is crazy durable.