"Auto-Size" fonts depending on number of incoming edges
In many circumstances I've encountered, it would be really helpful to visualize large datasets when you could automatically adjust the sizes of the nodes depending on the number of incoming (or outgoing) edges. Like, in
x -> a y -> a z -> a
the text and therefore also the node "a" would be 3 times larger than any x, y or z node. When you have like 10000 of incoming connections into a, then every other one may be only a little, nearly invisible bubble.
As I've said, this would be of great help and I believe this is technically easy to realize for somebody who knows about the GraphViz code.