RATHER AMAZINGLY, typing just eight characters into just about any application on an Apple computer running Mac OS X 10.8 Mountain Lion will crash it.
Open Radar documents the bug, which is triggered when you type "File:///" (without the quotes), though comments there indicate that other combinations of upper and lowercase characters, perhaps typed quickly, can also crash applications under Mac OS X Mountain Lion - seemingly any applications, including the Crash Reporter.
We tested out various applications on our Mac running Mountain Lion, and found that some but not all crashed.
Apple’s Text Edit word processing app, and the Safari and Chrome web browsers all crashed when typing in the text, while Firefox was unaffected. Microsoft also seems immune to the issue, with Excel and Word both unaffected.
Typing the same sequence of text onto a Mac running an older version of OS X did not cause any crashes.
The best Apple fanboi comment about this that we've seen so far said, "This is actually a feature. It allows you to shut down all applications before shutting down your Mac." Steve Jobs would be proud. µ