I bought my 92FS in spring/summer 2001. The only plastic are the grips (which I promptly replaced w/ Hogue). I saw a couple of M9's in a shop the next year, the differences I can remember were M9 markings on the slide/frame, finish was not as nice (looked & felt like parkerizing), came w/ 2 15rd (pre-ban at the time) mags, and the guide rod was plastic.
A word on my Beretta: It's the first gun I bought, I'd estimate it has fired ~ 10,000 rounds, and has never malfunctioned (unless you count the shitty alum-cased russian Silver Bear ammo I tried to feed it once - 2 rounds from the first box jammed, so I gave the other box away). If I let it get really dirty, it will sometimes fail to go completely into battery on the first round of a mag (spring pressure only, a tap on the rear of the slide finishes the job). I picked up a copy of the military TM for it and have detail-stripped it for cleaning 3 times, but have never replaced any parts (not springs, not pins, nothing) although I know I should. I love that gun.
--cfors