So just how significant an advancement is the 1D Mark II? My digital adventure began with the Canon EOS D30. Canon's first "affordable" DSLR. At the time Nikon had Canon trumped with the D1 "pro" digital body, yet there were many professionals shooting with the D30 as well. The D30 had a decent looking file, but pretty horrible autofocus by professional body standards. Yet I as well as many other Canon shooters made it work, because there was no alternative. You learned to work within the camera's limitations. When the 1D was announced, it was a Godsend. Every sports shooter snapped one up as soon as you could get your hands on one. It was a "must have" if you wanted to stay competive. All of a sudden those shots you knew from experience weren't even worth the attempt to capture became available.
So does the 1D Mark II offer another incremental jump in performance? Is it a "must have" to stay competive? Two easy answers...yes and yes. The much improved high ISO performance alone is worth it's weight in gold for sports and low light shooters. Pay attention to your newspapers, I think over the next 6 months you'll start seeing a marked improvement in the quality of images you see published. Just as the 1D offered shooters new opportunities over the D30, the 1D Mark II offers the same over the 1D.
If you can't tell, I am mightily impressed. Canon has hit one out of the park.