To add to this, I spent a long time doing a lot of UML. It was very much in fashion at my first job along with the Rational Unified Process (shudder).

I still use aspects of UML to this day, but I haven't used a UML tool in about 5 years and I probably couldn't tell you what the official spec is for arrows relating to association vs inheritance, etc.

To frob and ApochPiQ, I think you both have valid points in that yes, everyone uses UML-esque diagrams and no, most people don't follow the UML spec, but I'd argue that both of you have missed the point of the OP.

It wasn't about whether you use UML and/or other diagrams, but whether you do so on your own.

Personally, as frob said, the primary use of UML style diagrams is in communicating, especially to non-technical people. However, I will still whiteboard out an entity relationship diagram if I am working on something particularly complex, especially when dealing with legacy code (with new code, I prefer to keep the relationships as simple as possible)

I prefer a whiteboard to a software package or paper. Software feels like it should be saved as documentation (or at least, that's how other people perceive it) and paper cannot be modified easily.

i can work out most designs in my head.

occasionally i'll do a little pseudo code in comments first, or brainstorm on paper in the design doc.

if all else fails, its pen, paper, and the good old fashioned flowchart. but i have only had to do that a few times in many years of game development.

as you get more experienced, you need to document less, because you can keep more of the design in your head, due to greater familiarity with the design in question, and such designs in general.