Don’t Break Emacs Shortcuts
Native apps can “break Emacs” too. I just reported a bug in Sublime Text where ^K (kill to end-of-paragraph) doesn't work in the text field in its Save dialog. I suspect this is because, for some reason, Sublime Text explicitly maps ^K to an item in the Edit menu instead of falling back on the default Cocoa behavior.
Update (2012-09-23): Thanks to Andy Lee for noticing that I had originally misattributed his post to Andy Kim.