I just wanted to add that it is possible to touch up nicks, scrapes, and rust on a bike frame and have it come out looking really good. Art and antique restorers do something similar all the time. The problem is that this requires two things: 1) the ability to exactly duplicate the paint color and texture; and, 2) the skill to apply the paint so that it matches the rest of the frame. Most folks just go to the auto parts store to by a can of Dupli-Color that comes close and the brush or spray it on. The result is usually awful (though it will usually stop rust progression).