FismanLee said:

I think Yoda should always be on Dagobah, even in the prequels, and the Jedi would sometimes go there to be trained.

Bingowings said:

If that were so wouldn't Palpatine send his troops right there and kill him?

It makes more sense if nobody knows where Yoda is in the PT (he has become an exile for reasons best known to himself).

Maybe Obi-Wan finds out at the end of the PT and lands there to seek guidance.

Maybe because Yoda is so powerful he could bring down/tear apart Star Destroyers (you know, like the lesser powered unknown Jedi you play in THE FORCE UNLEASHED)? Hell, maybe that's the real reason the Death Star was created - to destroy Yoda.

Remember: Yoda is essentially the equivalent of Pai Mei, the demon master. He lives out in the woods; you can't find him unless he wants to be found; he appears as an old man, but can do supernatural things; etc. Palpatine could have either known or finding Yoda's location could have been a major plot point (the Jedi hinge on Yoda's training and existence). It could have even been the ulterior reason for building a clone army. That doesn't work so he builds a few Death Stars.

Maybe Palpy was a rejected student who wanted to match or supplant Yoda as "master of the universe" and has been seeking revenge for all these years. STAR WARS is in no way derivative of Shaw Brothers martial art movies, in which nothing like that ever happens.