Overall, I think it was a good idea. The CPU is located right next to the cool air intake. To channel this air efficiently, the thermal unit on top of the CPU directs the cool air immediately to the hot processor, then sends the heated air directly out the back of the case. This is far more efficient than ATX's way of dealing with unwanted hot air, which is to simply blow it into the case to eventually make its way out. A great way to cool your machine, and they run quieter and then most ATX PC's. Too bad Intel stopped making boards after the 965 chipset. I would have loved to see btx take off.
Examples:
http://ookaboo.com/o/pictures/noindex/picture.original/12641995/BTX_form_factor_motherboard_inside_a_Del
http://extranet.globalspec.com/InfoPreview/GlobalSpec/E360/Teardowns/Dell_Q965_Micro-BTX_Motherboard_%28iSi%29/Dell_Q965_Micro-BTX_Motherboard_%28iSi%29_-_Top_View.jpg
Examples:
http://ookaboo.com/o/pictures/noindex/picture.original/12641995/BTX_form_factor_motherboard_inside_a_Del
http://extranet.globalspec.com/InfoPreview/GlobalSpec/E360/Teardowns/Dell_Q965_Micro-BTX_Motherboard_%28iSi%29/Dell_Q965_Micro-BTX_Motherboard_%28iSi%29_-_Top_View.jpg