Not to conrtradict, but as others have said, Disney may write the guarantee on your resort confirmation and may tell you on the phone you are guaranteed. But its not always the case. I agree, they do try VERY hard to make this always happen, however its simply not possible that every request can be met. Flip over any "guarantee" Disney gives you and you'll see they put on there they only guarantee you a room someplace on property. There have been disboarders who had taken care of this by phone, with linked reservations under the same name who didn't get this request met.
Again, odds are good, especially if you have kids outnumering adults, but even in that case it can and does happen that the rooms are not connected.
In the case of our friends at ASSP (two adults, three kids), they were able to move rooms into their stay, but the first few nights had mom in one building with one kid and dad in another with the other two.
I am so glad Music has the Family Suites and wish other values and maybe even the mods would add some in as well.