Yes me since a few days!
Although the difference is not huge, i can clearly see it. I don't use Windows via Bootcamp, so i can't help you with that, but i do play the Mac version of Call of Duty 2 and 4.
First of all, i'm really glad that i'm again able to play Cod2 again. (Cod2 doesn't work properly with the 8xxx and 9xxx series of nVidia graphics cards - see other topic called "Call of Duty 2 LAG" for more information). I can play that game with maxed out settings on my 20" ACD (1680x1050 res.)
In Cod4, i play with higher settings than before. I now play with 2x anti aliasing, all the texture settings on High, the other settings all maxed out (i don't use V-Sync though), and it plays smooth enough for me most of the time. In some big maps (like Creek) the frames can drop to 30 fps, so i might lower my settings a little in the future, but till now it's looked promising.
Furthermore, i'm more a ATI fan than a nVidia fan. ATI cards seem to work better with OS X, the built in graphics (like opening Dashboard) stutter less than with the 8800GT.
So for me, this card was definitely worth the money and the 2.5 months waiting