Lately i am heavily using Firebug for my YUI debugging issues. And one thing really impressed me. You can inspect objects by "mouse-over" events in the source code. So there is rarely a need to define a watch on something because you can just use the mouse. Then a few minutes ago, i ve seen some Apple Xcode Videos and they have it too. Even though i dont think Xcode is the best IDE in the world, here it also shines.
Now the big question. When will _my_ IDE -> IntelliJ IDEA will have i? I have not checked out latest EAPs but i hope they will include it.