I love it. For those of you on the fence for upgrading to the 1D MKIII, you need to do it... but with a caveat.
I have my 40D gripped, played with the 50D, played with the 5D classic, played with the 5D MKII, and just picked up the 1D MKIII. I shoot strictly on AI Servo and center point with my 40D. I like fast moving shots, point/compose/shoot. So, far the 40D was doing great for me, and I always ALWAYS ALWAYS lusted after the MKIII. I never understood how awesome the ROF and 45 point AF system could be... then I got the MKIII (awesome prices now, they're such a steal).
Well. I'm in LOOOOOOOOOOOVE. I set up the Ring of Fire autofocus, and I am shooting just like I did with my 40D except my recomposed shots are tack sharp! The AF is that good. Add to that the built in grip, quick shutter lag, and all the other goodies the 1D throws in and I'm having a hard time justifying keeping the 40D and grip. Seriously, I think the only reason I would keep the 40D is the use of my 60mm macro for my intraoral dental photos... It seems a bit ridiculous to use the 1D for that purpose (and have to sell the 60mm and buy the 100mm).
But the 700+ I'd gain from selling all my 40D gear would be nice. However, keeping the 40D for the extra "reach" is nice considering how great of a body it is. It compliments the MKIII pretty well.
Now, those of you on the fence between 1D MKIII and the 5DII... I've used the 5DII, and It's really NICE!!! However the after using the MKIII I can see which one suits me. So, my advice is to try them both for a day. Find a friend that has one, or both, and can show you how to use it/them to its/their potential. Cause my friend swears by his 5DII.
For me the MKIII is that amazing. I'm itching to see what the next gen will offer, but I wouldn't be able to afford it now.

!
)
