Excellent concealed carry piece, if that is your intended use. Depending on which grips it comes with, you may want to try a few sets to determine which prove the most comfortable shooting and carrying. (For my money, S&W's current "fish scale" rubber boot grip, though pedestrian looking, is functionally excellent.)
Accuracy (the shooter's, not the gun's) increases noticeably after gently smoothing the internals. If this is a defensive piece, I'd leave the springs stock. If you have to tinker with the springs, keep it to the rebound spring and leave the mainspring alone. If you have to tinker with the main spring, test extensively with your intended defense ammo.
Practice...a lot -- all firearms need it, but snubbies especially.
Consider the 642's brother, the 442 Moon Clip; comparable price and factory cut for moon clips, which are terrific for fast, easy reloads (five shots go fast).
And to answer your inevitable next question:
1) CorBon DPX 110 grain +P
2) Speer Gold Dot 135 grain +P
3) Buffalo Bore 158 grain SWJHC standard pressure
