With a simple macro ...

Code:
/script DEFAULT_CHAT_FRAME:AddMessage(GetXPExhaustion());
... you can see how much rested xp you have in your chatscreen.I have this hotkeyed on all my leveling toons, takes me 1 push and a look at the other screen to see my status. If jamba could do this, would even be better.

For myself i'd find a special addon with a webinterface overkill.