I'm not, as far as I know, descended from John of Gaunt, but I do have one line which was in dispute with him for decades, leading to at least two murders (supporters of Gaunt killed by my ancestors, the Stathams of Morley, Derbyshire).
More recent members of the same family were descended from King John via an illegitmate child of his second son Richard. Obviously once you make a connection to royalty, your ancestry suddenly stretches back well into the first millenium, but personally I tend not to put too much effort into studying such well trodden lines - I prefer to concentrate my efforts on lines which feel a little more personal, and from which I can get the enjoyment of discovering the links for myself.