I've fielded three different M9s during my military career, and other than the slide markings, plastic guide rod, and bar rear sight, I found them to be indistinguishable from my 92FS. I've heard there are some differences in the dust covers, but I never noticed.
As for the comments on the trigger, I'm nonplussed. Other than the ever-present DA/SA debate, I've always found the 92FS/M9 to have one of the smoothest triggers I've encountered, even the boat anchor/future paperweights issued to me by Uncle Sugar. The DA pull is admittingly typical of the breed, but the SA is sweet as can be.