I certainly hope this is the right place for a thread like this, and I apologize in advance if its not; and, for that matter, if this has been brought up already. I didn't see anything about it in the next few pages.
So, it appears that the Valley map, the one that allows the usage of only Infantry forces, has a slight flaw, at least from the Nod side. I've discovered that, from the Guard Tower closest to the Hand of Nod, it is possible to shoot at the GDI Barracks, allowing, say, Rocket Infantry, to quickly wipe out GDI's ability to produce advanced infantry units.
I'm afraid I don't have screenshots at the moment, as I couldn't figure out how to make that work, but I can try to get some up if necessary.