I have had the luxury of moving into a brand new home two years ago, which has a media room upstairs with an attic above it. I had the room pre-wired for a 5.2.2 setup but ended up re-wiring it myself for a 7.2.4 setup. I actually have SIX speakers in my ceiling as I couldn't be ahem'd to fix the holes in the plasterboard ceiling that would have resulted from re-using the original two in-ceiling speakers. Future proofed is what I told the wife...
I could, repeat could, conceivably configure our media room with two fronts (proper stereo speakers), two front heights in-wall, one or two centres, two down each side of the side walls, two rears and six overheads, plus up to four subs, for a total of a 12.4.6 setup! Would be overkill in a 12'6 x 20' room though....
Downstairs in the living room I had the ceiling pre-wired for a X.Y.4 setup. With 20/20 hindsight I should have had them pre-wire for a rear pair as well, plus and have a power outlet and a conduit put in over the fireplace in case I wanted to put the TV there. I could have convered the outlets with a picture in the interim. I can't use sides in that room as there aren't actually any side walls to put them in or against (one wall is all window, the other is open plan to the kitchen and therefore doesn't exist), so the maaximum I could go in that room would probably be a 7.2.4 setup.