From what I've seen of active duty M9s, a steady diet of mil-spec M882 9mm (which is +p-ish pressure levels) will eventually crack your locking block, which in turn will probably damage your frame and predispose your pistol to breaking further locking blocks. However, changing your recoil spring more prudently military maintenance schedules, like MadMerc mentioned, will help with this.
Personally, I'd run standard pressure through the gun for range work (cheaper anyway) and save +p for real duty use (+/- some rounds to verify your specific load/brand/etc work) and you should be fine.