Coversational putty, used mainly on IRC to smoothen the flow of chat. Can be used to acknowledge another person's speech, while not actually responding to it. Can also be used as an equivalent of throat-clearing, indicating that you have something to say which will follow afterward.
<Jimbo> so I just said forget it and went home
<llama> you guys won't believe what just happened
OK, I'm Argentinian people, here's the real deal: Che is actually used mostly in Buenos Aires, the capitol. It's not true slang, it's just a word used in Argentina. Slang is more common in the inland regions, like Cordoba. Che means either "hey" or "buddy", or simply "hey, buddy."