Yeah, I also would like to see some kind of list with effects. There is totally 0 explanation in the game.

Hidan got the Tag debuff too.
Its kinda rare indeed, but some have it.
Tag debuff reduce the tagged enemy's Def & Res by 30%.
Also some ninjas skills will work after enemies which are tagged, example Raikage.

Siugetsu has it too.

if you are looking for an official guide, can't help with that
but these are the effects of the conditions, same for all versions

poison - makes ac*ulative damage to opponent
ignition - causes damage to opponent and makes healing ineffective
chaos - opponent will attack his or her own team
immobility - will not be able to move (use mystery or normal attack)
sleep - same as immobile
acupuncture - cannot use mystery/ cannot move
paralysis - cannot use chase attacks
blindness - cannot use normal attack
celestial prison - using charkra will cause damage to character
interruption - cancels the mystery
tag - reduces defense & resistance by 30%

nice,this sht helped a ton lot my *

Good list, but a little more info can be added.

poison - makes ac*ulative damage to opponent, can be stacked up to 4 times.
ignition - causes damage to opponent and makes healing ineffective, cannot be stacked.
chaos - opponent will attack his or her own team
immobility - will not be able to move (use mystery or normal attack)
sleep - same as immobile, but can be undone by tajutsu.
acupuncture - cannot use mystery skill, can be used as an interrupt
paralysis - cannot use chase attacks
blindness - cannot use normal attack
celestial prison - using charkra will cause damage to character, will not kill though
interruption - cancels the mystery
tag - reduces defense & resistance by 30%, allows some ninjas to enhance their mystery

http://forum.naruto.oasgames.com/en/forum.php?mod=viewthread&tid=6570&extra=page%3D1

Shameless adverti*t, maybe it will help :D