I haven't noticed to much flex but the bottom plate is not flush with the keyboard chassis. You can run your finger along it and feel the edge of the plate. It's somewhat of a nonissue because the rather large feet also sit out slightly so the computer is very stable when sitting on a desk.
The weight is distributed well when the machine is open, which is nice because I often have to move and turn my computer to show coworkers information on my screen or to have someone fill out a form or authorization.
When the machine is closed it feels like a fairly flat and solid piece of metal. It carries well and the finish, at least the Starlight finish, grips well. I appreciate that because I have a bit of nerve damage in my hands and my grip is not what it could be.
I've used the computer on my lap in my recliner. I'm a fairly big dude so it's not that awkward to use it like that. A smaller person might find it uncomfortable to use the computer that way though.
It really is a nice machine, assuming a 15'' consumer laptop is what you are looking for. Since the most intense thing I do is play old games on OpenEmu, I'm not to concerned about the CPU or lack of active cooling.