I experiment some with pie crusts and have seen recipes that include vinegar as well as eggs. What does the vinegar do and what does the egg do. I have heard the vinegar promotes tenderness but have read on one of the posts here that it speeds gluten formation.
From On Food and Cooking:
Acidity in the dough - as from a sourdough culture - weakens the gluten network by increasing the number of positively charged amino acids along the protein chains, and increasing the repulsive force between chains.
And weaker gluten structure is definitely a good thing for pastry doughs!
From the same source:
[Eggs] supplement gluten structure with tender protein coagulum, tenderize products; slow staling
So eggs help provide a more tender structure, again good for pastry doughs.