As pstoller stated, a tux is a tux, and a black suit something else altogether. Having said that, there are plenty of black suits out there which will do nicely for less formal evening affairs, especially in our dressed down age. Neapolitan cut suits, especially, with their high cut airholes and suppressed waist, are especially suitable. Personally, I own a peaked lapel three button black crepe suit which I find to be a rather nice hybrid number, suitable for a variety of events. I prefer uncuffed pants for my suits as well as for my tuxes. I know that the extra material make pleated trousers drape better, but I prefer the clean, unbroken line of uncuffed pants. It's a compromise, either way. I have seen cuffed tux pants, but think that they look rather odd, since tux pants are generally flat front and cut slim to elongate the profile, and should break dramatically over your formal pumps. For the same reason, I think that besom pockets look much more appropriate on a tuxedo jacket than do flap pockets, which break the continuity of the jacket's silhouette. A tuxedo should look, as much as possible, like a sheath. Remember, it is a dramatic garment meant for the evening - its movement is infinitely more important than details like hand-stitching.