FWIW, every once in a while a new tube will come from the manufacturer with a slight bend in it. A knowledgeable builder will roll every new tube on a flat surface to verify straightness before using it in a frame. I make no claims of being knowledgeable, which is how a bent tube found its way into a frame I built a few years back. It's not bent enough to be noticeable unless you use that straightedge, and because it was built into the frame from the start, the end result is still aligned correctly, kind of akin to what Fuji86 is writing about.

Which is all a long-winded way of saying that the bend, by itself, is nothing to be concerned about. The frame can be aligned correctly and ride perfectly, even though the tube itself may remain a bit bent.