|Ian's analysis of synoptic similarities|
What Ian has done here (best read the post, of course!) is to compare when Matthew, Mark and Luke agree on specific Greek words in their shared stories about Jesus; this might indicate a shared source. The analysis is interesting, as you can see - it confirms a huge degree of interdependence.
Still, I think it's missing something. What we need is a co-analysis of where the various stories appear, and if there is any sign of deliberate alteration or correction of a more primitive text. For example, most scholars agree that Mark came first (or at least most of it), as its Greek is a bit "countrified"; Luke and Matthew spoke better Greek (both were evidently living in the Hellenistic world, not the Aramaic-steeped wilds of Palestine), and therefore corrected and sanitised Mark in a reverse process of that which Mark Twain used to reflect the dialogue of Huckleberry Finn.
I'm sure this has been done before, but one set of techniques which could be very helpful in sorting these things out would be to use some of the tools of modern bioinformatics, when we search and compare the genomes of different species to infer their evolutionary relationships. I'm going to toddle off to have a wee think about this, and may report back...