The left side of my casing also can be pushed in, but I was told that is normal. All of the display models do it at least.
My casing can also be pushed in around the display (this happens with relatively low pressure i.e. opening and closing- and has gotten progressively worse. I convinced Apple to have them fix it, although it came back quite un-fixed. I have to send it in again before they give me a new machine. They did give me a battery though.
On a slightly related casing note, I've noticed that after just 2 months of use the trackpad has gotten quite shiny. I understand this is inevitable in laptops, but in 2 months? Usually I see this in 2-2.5 years. Is this considered a defect and part of the whole casing and discoloration problems in MacBooks (something they will repair) or is it considered normal? Its not a big deal at all, I just wanted to make sure my lower casing wasn't a problem too.