As part of my job I model quite a few things. I'm familiar with serveral modeling languages, and the two I use most often are Business Process Model Notation (BPMN) and the Unified Modeling Language (UML). I find that a picture is worth a thousand specs, so I've been putting these model languages into play quite a bit.
Before I came to Microsoft, I used StarUML (no relation to Star Office), and really liked it. I can't use that here because it would open up our code to the GPL license, and of course I can't do that. So I've been looking for a replacement, and I haven't found one I like as much. I'm currrently using Visio to do the drawings, but I'm not as fond of it as StarUML. Ah well, perhaps it's just a learning thing.