I do quite a lot. I use it for sketching out and documenting software. I use state machines for, well, state machines, which make up 90% of the software I write

I do quite a lot. I use it for sketching out and documenting software. I use state machines for, well, state machines, which make up 90% of the software I write (embedded). They can almost mechanically be transformed to sourcecode, but I do the coding by hand. I use it for sequence diagram to sketch out and document sequences of events, and also generate sequence diagrams out of trace logs. And finally I use class diagrams to document the software architecture. For all of these I use plantuml because the text format is simple, human readable, and easily versioned. For the kind of software I write (embedded software with a lot of state machines and strong OO architecture), it is absolutely great. Definitely one of the big tools in my toolbox.