As a parting thought, here's a list of interesting features you might want to examine more closely:
Rethink Orthogonal You can change the default straight, diagonal lines in the Diagram Editor to orthogonal lines by pressing Ctrl+O. You can also force ModelMaker to try to find the shortest possible orthogonal path for a line by pressing Shift+Ctrl+O.
Visual Styles Manager This manager (available in the shortcut menu of the diagram view, under Visual style ® Style manager) deserves an entire section. Take some time to check it out. You can define a wide variety of hierarchically related visual styles for your diagram symbols and apply them on the fly. Also, don't forget to click the Use Printing Style button in the Diagram Editor to strip out the non-printing elements and see what the diagram will look like on paper.
Design Critics Design critics are an impressive QA feature in ModelMaker. They are little proofreaders running the background, checking out your code. To get at them, make sure Show Messages is enabled (Shift+Ctrl+M), right-click the Message view, and select Show Critics Manager. I advise against turning off the time-stamp-checking design critic, because it will warn you if the source file on the disk has changed outside of ModelMaker. You can also create your own design critics via the ModelMaker OpenTools API.
Creational Wizard This is yet another nifty bit of automation for the busy Delphi programmer. The Creational Wizard (available from the Wizards button in the Member List) checks the model for class members that need to be instantiated or freed and adds them to the appropriate constructor or destructor. It will do a few other things too, and there are some caveats; press F1 while you're in the wizard to access the online help.
Open Tools API Much like in Delphi's Tools API, this ModelMaker feature allows the creation of plug-in experts for ModelMaker. The API is robust and includes access to diagrams as well as the entire code model. The possibilities for extending ModelMaker in this way are extreme.