Although it's quite nice, it comes as a jar file and so requires local Java to be installed. I have looked around for some mechanism to package this up in to a single executable but have not found anything really suitable.
This is more debatable now that the documentation isn't built unless specifically enabled and installing Java is not a high hurdle. If I'm the only one who builds the docs locally I am OK with this. Or, if some one can package up plantuml.jar without requiring Java, that would be cool as well.