The 630i isnt BTX as far as i know, im pretty sure its just inverted atx.
http://www.driverheaven.net/reviewimages/dell630i/pictures/hardware/overviewinsidecomplete.jpg
BTX Motherboards would have the i/o panel at the top and pci/pci-e connectors at the bottom, inverted ATX is just an atx motherboard mounted upside down.
If you're looking for any negatives in that case, the green trim may put you off and it's a bit shapeless.
i like teh green and the boxiness is another thin i like about it