The new (detachable) frame toolwindow is great. And it assisted me greatly with identifying recursive calls and showing the debug markers.
I have a suggestion, which would make it even better - provide a way to identify an object instance in the frame window, i.e. the Variables view displays the hashCode.
I was debugging a crazy recursion with concurrent threads recently (don't ask even ;), and that one feature would've saved me many pains. Otherwise I can't tell the difference without putting a marker, but markers do not persist (naturally) between debug sessions.