I agree, I always call the dispose method if implemented. I couldn't find the handle leak in your test app. The handles do increase but when a GC collection occurs (for me I had to create about 30 dialogs) the count returns to what it was initially?? This is because the finalize method is executed which in turn calls dispose.

The Form class is implemented correctly, it inherits from Component which calls Dispose(false) from the Finalize method. The Form class overrides the Dispose(bool disposing) method and has it's own clean up code in there [which in turn calls the base class dispose(false)]. Which is the documented way of implementing IDisposable.