The only uml diagram I've really used in the last decade or so is the sequence diagram - for describing use cases for network message exchanges. And even that is in powerpoints and on whiteboards. I can't imagine ever formally documenting anything that way. Too bulky.

I try to avoid over-use of inheritance, so class diagrams don't get used for that. Mostly I use unstructured boxes and arrows for entity-relations, and don't worry too much about notational rigour.