It is assumed that the Force is guiding all of your actions, so everything you do is particularly well done because of your reflexes. This is why I've had people remove "reflexes" from their skill list, because it's redundant. 

Perception has a few uses.  For stealth, if a character is hiding, you'll roll your perception against theirs(unless they actually [i]have[/i] a stealth skill, then that character would get to use that) to see if you can spot them in time.  

In the event of a sneak attack, yes, you would roll perception [i]before[/i] rolling combat.  If you pass, there is no penalty, if you fail, you'll lose a few dice in your defending roll.  Actually, I'm going to come up with a scale for this to make sure it's defined for the event that it happens.

It's also used for GM purposes.  If I or TheUnknowable decide there is something hidden in the scene, we'll roll everyone's perception to see who sees it.  If no one sees it, too bad.