The Hardcard wrote in post #3895420
On the grip. What is so bad about it? I read about the Nikon grip and the only advantage I see is that it allows you to use the camera battery in addition to batteries in the grip. A nice advantage, but in my eyes doesn't relegate the BG-E2N to joke or piece-of-you-know-what status?
Is their a big price differential, or am I missing something?
I didn't like the BG-E2 before the D300 came around, so it's not a matter of it being ok before but suddenly awful because something better comes along.
AFAIK the BG-E2 is mostly plastic, whereas the D300 grip is magnesium alloy. I think the D300 one also has a nice rubber layer on it that matches the rubber on the D300 itself.
The D300 grip allows the use of D2X/D3 batteries. As I said in the "D300 preview" thread, imagine being able to use 1DIII batteries in the 40D grip. Ingenious, I say.
The curve of the D300 grip also looks very similar to the D300's built-in grip to match it in terms of handling and comfort, whereas the BG-E2's isn't as comfortable as the 20D/30D's built-in grip, or the 40D's I'd imagine.
Lastly and least of all, it just looks like it belongs on the D300 because it's molded to follow the contours, whereas the BG-E2/N looks like it's a haphazardly stuck on box. I wish I could say, "BG-E2--they're boxy, but they're good," but I can only get as far as "they're boxy." 
Of course with all the metal in there the D300 grip might cost $200+. Who knows.
On the AF, the thread with the very shallow DOF cycling shots shows that the 40D AF system is fantastic. Maybe the pro AF systems do better with a lot of criss-cross motion, but for straight up tracking, you'll be hard pressed to show an advantage of the pro AF systems - be they Nikon or Canon. Also William Castleman did a tracking test on semis coming at him at freeway speeds. Out of 50 servo shots, 47 40D shots had sharp, correct focus - versus 48 for the 1D Mk II and 40 for the 20D.
I'm pretty excited about the AF on the 40D--supposedly 30% faster AF calculations than the 30D and all AF points are cross-type. This is a big step up, although I'm still not a fan of the diamond layout.