I can't remember where i got this information, but it says that this technique will cook the rib perfect everytime. I have only tried it once, but it did come out perfect. In fact I read this post just after getting back from the store with a prime rib that I planned on fixing tonight. I put a rub on mine just because the boyfriend likes a lot of flavor.
rub (should be consistency of a scrub)
1 T. salt
1 T. sugar
drizzle of olive oil
apply on room temperature roast
Turn oven to 500 or highest setting. Take the total pound of roast and multiply by 5 to get the timeing (for example you have a 2lb. roast you cook it for 10 minutes) Then turn oven off and let it it for 2 hours. Don't open door- roast is still cooking. This will come out a perfect medium rare.