In the last 6 years Omondo has been permanently improving
the use of
SWT for creating UML diagrams.
SWT is a lot more flexible and powerful than Swing.
Directly using native SWT API allows to manage huge graphical diagram
manipulation
without freezing your windows.
Directly using the core of GEF and EMF API is also a lot more powerful
than just using the GMF plugin
.
If you try EclipseUML 2011 you will see the difference when modeling
large projects.
No freeze, no memory crash etc....