A problem I had with my 2006 MBP was with the way the ?top case? attached to the ?bottom case? (dunno the correct terminology). These were attached with flimsy aluminum tabs, which in my case and other cases i've heard of, some have eventually broken due to just a small amount of flexing over time. Apple would not fix this for me under applecare. ("improper handling," as though i should carry it around like a small infant...)
I suspect that the unibody design is more robust, and does not have such flimsy attachment points. However, I haven't actually looked to find out. When my new 15" i7 antiglare arrives via FedEx today ( 😀 ), that's one of the first things i'm going to check out.