Over at Remnant of Giants, Deane Galbraith has a good post on Luke knew Matthew, But Still Q.
In The Gospel of the Lord I’ve advocated this and called this view the Holtzmann-Gundry Hypothesis (HGH) to the Synoptic problem (I hope it catches on). It rests on the idea that although Luke used Matthew, Luke and Matthew might have had sources common other than Mark, including some oral and written materials, especially in the double tradition.
In conclusion, the dependence of Luke on Matthew does not determine the question of Q’s existence. The Farrer Hypothesis’ compelling challenge to the Two-Document Hypothesis may, rather, be the first step in rehabilitating a reappraised Q.
I think this is an interesting angle worth exploring for those who are, you know, in to that kind of thing!