I don't know if you've played a human before but perception never was something to brag about. Most of the time you would see a rogue when it was already too late to avoid the incoming sap. Also it felt almost like you could only see a rogue when he was stupid enough to approach you from the front, but then again, I bet any other race would see them coming then as well.
In the days when perception was a skill with 2 minutes cooldown however, it was kinda cool, it felt like it really did make a difference, of course you would only see a rogue when it was already too late as well