Too bad you bought Canon, whose EF-S lenses will not even MOUNT on their FF bodies...Nikon's FX bodies WILL mount and WILL shoot the Nikkor DX lenses, either at reduced megapixel count, OR with almost full-frame coverage in the 4:5 aspect ratio on the D3 series bodies...as Nikon showed, there is no real reason that a reduced-circle lens must be made so that it will mount ONLY on crop-frame bodies....as Nikon proved, a reduced-circle lens can easily be made so that it works on ANY camera body currently made...
As to the worth of a 5D-II with a $389 EOS Elan body paired with a $2,000 sensor....hmmm....the sub-systems (simplified extremely centrally-weighted autofocusing, color-blind metering, no built-in flash, no flash commander, slow FPS, poor light meter readouts for use in bright light) ehhhhh....I can see how many people do not see the value proposition in the 5D series. It's another matter entirely if you're looking at a Nikon D700 at the SAME price as the Canon 5D-II....there you're getting a camera with a full-bore professional autofocusing system, color-aware light metering for both daylight and flash, built-in flash, built-in flash commander system, faster FPS, and a rugged pro-type camera body, not a consumer body that has had a good sensor dropped into it. If you're looking for the lowest-cost, highest megapixel full frame d-slr, the SOny A900 and A850 are the lowest cost AND the highest MP models currently on the market, and are actually pretty nice cameras, with good viewfinders, and actually quite nice ergonomics and 'feel'.
The value of a FF camera depends on what you need it for, and to an extent, on which camera maker you buy it from. Canon, Nikon, and Sony are all selling very different types of FF d-slrs at the $1899-$2600 price points. FOr people photography, I prefer the "look" of shallower depth of field, and the way FF allows me to use traditional focal lengths, in traditional locations, to get the kind of background control that is a total PITA to achieve with a crop-body camera.