Someone has asked for Visio diagram generation.
After some tries, we have added a flag "-tvdx" to the command line that allows to generate .VDX file that can be read by Visio. You can download it here : https://dl.dropboxusercontent.com/u/13064071/plantuml.jar
This is really an alpha version : many things are not working.
But this shows that Visio generation could be done.
Unfortunatly VDX format is not very documented. And it seems that Bezier curves/B-spline are not possible (any idea anyone?)
The VDX generation is not a high priority, so we will work on this only upon user requests.