Just discovered plantuml and liked it - i can use some visual aid if only i do not have to draw it.

Sequence and use case diagrams are useful. Class diagrams i would rather see in code.

I also misuse use case diagrams for arbitrary graphs. It is good to see if a graph i came up with looks too much like spaghetti. Helps to untangle it. But it is not proper UML and i could use the graphviz dot itself for it without plantuml frontend.