We have had at least 90% of our requests for locations honored including CBR, POR, CSR, AKL and WL. We usually keep the request simple - building or "near" something.
When we checked in at Poly once she had marked Aotearoa on our map (we requested Tokelau) and was just about to give us directions when she looked at her screen again and showed me that the room was in Tokelau. When I mentioned "Oh, not Aotearoa?" and she replied "No, because we requested better room". So the request system works - sometimes. Last December we stayed at Poly again but got a little too restrictive in our request (asked for Samoa, ground floor, facing pool). We ended up in Rapa Nui in an accessible room which we did not want. Couldn't sweet talk the CM into anything closer. In fact, while both CM's we talked to were not outright rude they were not very friendly. This did not ruin our stay, however. On the same trip earlier at POP we got EXACTLY what we asked for.