Kambiz,
TSimpleGraph has so much potential that every time I look at things I can see places it would be better.
Here is one example where some nodes are held in a container node.
http://www.allroundautomations.com/plsdiagram.html
While this is a database schema, there are various similar applications where this sort of thing would be most useful --hierachy diagrams where there are departments/divisions/regios etc.
The only significant thing about this container node object is that it 'contains' other nodes. Which basically means one simple thing: The 'contained' nodes move with the container. That's about it.
Do you think this is hard to implement; would you consider that sort of a thing for a later version?