A friend turned me on to them several years ago. While I haven't see the Mekons themselves, I've seen Langford in various solo incarnations countless times. Never fails to entertain.
He's an accomplished artist, too. Exhibits and sells his work through the Yard Dog Gallery in Austin. Great little place, BTW, if you happen to be in that town. Also has amazing 'back yard' concerts during South by Southwest every year.