I can't find a way to increase the number of available working set. When I pass the number of 8 working set, it is not possible to see them in the project explorer any more. When I go down to 8 thus I can see them in the project explorer.
I'm not quite sure what a "working set" is. You can definitely have more than 8 projects in a workspace and listed in the Project Explorer, though. In fact, it is my fondest dream that someday I'll be able to reduce the number of active and referenced projects in my workspace to only 8 or so.
An IDE is no substitute for an Intelligent Developer.