Li Shenron said:
			
		
	
	
		
		
			
Not to mention that a DM could rule that if the tripping AoO is successful, the "tripper" may get a second attack because of the other benefit of Improved Trip. 
		
		
	 
My point exactly -- except that this isn't a judgement call on the DM's part.  Rather, this is what the rules would unambiguously call for.  The combat would look like this:
Opponent with combat reflexes, improved trip, and a reach weapon:  I delay.
Poor Player:  I charge that mofo!
Opponent:  Ooh, an Attack of Opportunity, eh?  I trip him.  W00t!  He's down!  I use my extra attack to whale on him!
Poor Player:  Crap, that ends my turn, right?
Opponent:  I stop delaying.  I whale on him!  I whale on him!
Poor Player:  My turn again?  Fine, I stand up, step forward 5' --
Opponent:  Not so fast!  You stand up?  I take an AoO to trip you.  W00t!  You're down!  I use my extra attack to whale on you!
Poor player:  Crap!  Fine, I use my remaining action to try to stand up again, and then I'll move back 5' --
Opponent:  Not so fast!  You stand up?  I take another AoO to trip you again.  W00t!  You're down!  I use my extra attack to whale on you!
Poor player:  Crap, that ends my turn, right?
You see the problem.  Under the old rules, at least the poor player could have stood up, moved forward 5', and gotten a single attack off on the Opponent without fearing an AoO; as it is now, if the tripper's got enough of a tripping advantage, the poor player can never close in.
Daniel