I have just set up a development portal for CorelDRAW/Designer/Photo-Paint 3rd party developers. I hope this site would become a knowledge base for developers to go to for documentation, code samples, etc.
The site is at
http://dev.oberonplace.com/ and is running a wiki. It has the object model documentation for CorelDRAW/Designer and Photo-Paint. At this point, the "documentation" is just a set of pages generated from the applications' type libraries, but in the future I hope we all will help contribute to the documentation and turn this into a great resource with detailed description of classes and methods, code examples, various tricks on using objects and methods, and so on.
Everybody is encouraged to play their part in expanding the documentation and contributing their knowledge/experience to the site.