Final three is right, but thats not what I meant. I trim for 75 knots which is the recommended approach speed and leave it there. The Piper Arrow POH actually states you should do this and I think the Warrior POH does the same (or is it 70?).
Vref for the PA28's I fly is 63 knots, and that is what you should come over the fence with, pulling back a little on the column to get to that speed.
Its important to stick with the POH speeds because matter such as elevator authority, the ability to retract flaps without stalling if you have an engine failure on final, control column forces in the event of a go around, and probably a heep of other stuff I can't remember, all depend on the speeds and attitudes you adopt.
To put it another way, I guess you could approach and land at Vs + 1 Knot, but if anything goes wrong.........