Maybe it depends on which browser you're using, but in Safari 5, when the main textbox/input box has focus, C-n works for me, as well as ESC for Meta. You may want to try giving it focus first?
Strangely (ironically) Ctrl-N works fine in Safari (on Windows), but Ctrl-P brings up the "Print" dialog. In Chrome Ctrl-P works fine, but Ctrl-N brings up the "New Window" dialog.
Both work fine in Firefox.
Who said that one of the best things about developing web-apps is that the apps are cross-platform?
Hopefully it's equally broken in different ways on various browsers on OS X and Linux. ;-)