Just came across this discussion and thought I would place my "two cents" in.
My experience has been the opposite of JANERG .
I use points and certificates throughout the year and can't remember an incident where I wasn't treated as a paying Platinum guest.
If the use of points is for a vacation I usually call ahead to insure that I receive the accommodations and/or upgrade that I was expecting.
For once I have something positive. I have used my points in a couple of Marriotts (Laguna Cliffs, CA, Provo, UT, and Carlsbad, CA) and a Residence Inn. On all of the occasions I have been treated well. All of these stays have been for personal reasons and special occasions as gifts to my grown children. For these I make sure I call the hotel ahead of time and tell them what's happening. My guests and myself have been pleased with the outcome.