From the informative web site Hotel Reviews, Hotel Ratings, Hotel Openings || HotelChatter (which as you see, is highlighting Marriott's and Ian Shrager's new Miami Edition - boy, the press loves Ian), here's a good overview about room assignment.
As Sy Syms used to always say, "an educated consumer is our best customer" (which may not be Marriott's tagline ), arm yourself with info. Read the part about front desk range of autonomy. My conclusion, if you want something - communicate. If you just wait and expect your just rewards, whereas sometimes it will work out fine, often it may lead to you being slotted in an acceptable ( granted, which is often good enough, I save contact energy on many trips) to help them provide others what they asked for. Like many Insiders, I agree that for the most part, FDAs and hotels in general want to please their customers as much as sensibly possible, but they need to know. What say you?