I would agree on the most part about counter jungling. If you leave behind small monsters, you gain less experience too, but if you take everything, sometimes the monsters respawn before the enemy jungler get around to them (like VI who tends to gank early then head to other camps).
I have been counter jungled, but unless they take Red or Blu, it rarely makes a difference to my game. I still get hurt more if an ally jungles (usually an ally takes my jungle AND I get counter jungle'd and the ally then complains I don't gank :/)
There's so many camps now, it's easy to make up for lost exp, and cycle around to let lost camps respawn. Counter jungling is only effective if:
a) you get a kill or very good ganks (coming from enemy jungle you often find blind spots)
b) you take multiple camps - which is dangerous as you extend your time there and are more likely to get caught low, you really only want to do this WHILE you have eyes on all enemies, then you can clean up everything
c) taking the enemy big buffs
d) very early game, successful counter jungling will give you a strong lead, but most of the time laners' will cover jungle and drop some free wards, so it's still very risky
I find that if I successuly counter jungle and then gank, enemy jungler will gank too (and we'll still be near same level) but their timing will be better because they didn't lose as much hp farming so they are just waiting for you)
I prefer to farm their jungle, then predictively farm my own. Sometimes after stealing a red, an enemy just steals yours (especially if you get seen by someone hiding in brush or a ward) getting your jungle too will force them to gank prematurely, or waste time trolling your jungle looking for camps or you at low level, this REALLY puts them behind. Making sure your team know that you've stolen the enemy jungle and to watch out for early ganks is important too :D
is better than 
for counterjungling, you clear the camp about 4000X faster and you get hp/mana back.
exp gain passive in the enemy jungle?
