The M&P 40c is one of the most versatile guns you can buy. It's not too big and not too small. To me, the negatives you get by going to a smaller, more easily concealable gun, namely a smaller gun being less comfortable to shoot and less accurate, make the 40c shine, as it's not nearly as punishing to shoot as are the smaller 'pocket rockets'.
With practice, the 40c is fairly accurate out to 15 yards or more. By and large, that's where almost all self defense scenarios occur. With the gains made in critical/self defense ammo from companies like Hornady and Corbon, the 40 is a potent self defense round.
If the 40c weighed 3 or 4 ounces less, it would be more challenging to shoot accurately and with as much confidence. Like most, I'm a bit more acurate with 9mm, but in a self defense situation, I'd much rather have a 40 or 45 in hand.
I like using the optional full size magazine with the x-grip--it looks very neat--you can hardly tell the x-grip's even slipped over the longer magazine--it looks almost 'stock', and the extra rounds per magazine makes range time more satisfying. For C&C, the standard magazines, especially with the pinky extensions, work great.
I find the 40c to be much more 'user friendly' than my Glock 27 w/ pinky extensions is. Yea, the Glock 27 is a wee bit smaller and conceals just a little easier with less 'print', but the M&P 40c is so much better in enough other aspects that overall, it is the superior gun in my opinion.
Small handguns have improved so much in quality, comfort in shooting and accuracy in recent years. I find myself leaving my full size 9, 40 and 45 handguns at home more and more--they just seem like cannons in comparison. They're fun on the range and useful as side arms when hunting large game, but for most 'real world' situations, the M&P 40c fits the bill quite nicely!