Why the 40D is better then the D300 :)

Cheaper
Lighter
More functional wifi grip - with an ethernet port

Better sensor (yes, enhanced/v2 400D CMOS sensor. D300 is Nikon (Sony's) first CMOS sensor)
Better IQ (wait for reviews - none of the soft underexposed Nikon rubbish)
Cheaper and better lenses (17-55 2.8IS, 50-250 IS, 24-70 2.8L, etc.)
Looks nicer
Faster fps

The D300 has 50k more pixels, can control more flashes and has a bunch of other gimmics 99% of photographers will not need.

If I wanted to spend Nikon D300 money, I would spend another $400 and get a 5D.

no contest!