It would be great to see a timeline, where each method invocation leaves a colored point behind it. So there would be colored trails as time progresses. Then it would be useful to spot methods that are called too often. Or to quickly see the call stack. ESP if you could zoom in and examine the recorded history. That would be so much better than stepping through a debugger.

Also if it was injectable via a bookmarklet into a running backbone application. That would make it a great debugging tool.

Bonus points : click on a method to see the source code