I'm not trying to take business away from the aftermarket companies, but I haven't bought an M&P yet that had a trigger that wouldn't smooth out after some lube and a couple hundred rounds. I first fired an M&P 40 in something like late 2007. The cop who had it issued said the trigger wasn't great compared to Glocks. Which I'd been shooting and carrying for about 20 years at the time. Oddly enough, I didn't notice the negative qualities, and bought a new 45 in early 2009. Granted, all my M&Ps are blue label guns, but I judged the triggers were probably a pound heavier than the standard Glock trigger. My most recent purchases were two 9mm Shields last month. I noted one trigger was slightly more crisp than the other, but neither were out of line for a small, concealable, affordable-priced personal defense pistol. In all the time I've been interested in the M&P line, I've only seen a couple at stores that had really bad actions, and I didn't buy them. If the LGS will let you fry fire before buying and you're not comfortable, leave that one at the store.
My experience has found that a dry fire training routine will help a shooter get used to the trigger of his/her pistol more effectively than additional expenses and possible legal hassles in the event of a shooting or an accident. Work with and master what you're shooting/carrying. If you do ultimately decide to go with an aftermarket trigger, you're still obligated to master it. I have run some guns with trigger jobs over the years, but never really noted that they were absolutely essential and in themselves provided me with any great accuracy improvements. I have encountered a few guns over the years that came equipped with horrible, triggers that made the worst M&P seem like a custom job. Fortunately none of them came home with me.