Bread & butter - these products pay the bills, the challenge is to maximize profits and to manage them to their full potential.	Pearls - You have something!  It needs nurturing and everyone believes in the potential for this product.
White elephants - they take up resources for little return, especially when looking into the future.  But, they don't go away.	Oysters - you never know what you might get... The challenge  is to get them moving, either on way to being a business or out the door!

When you start thinking about your R&D budget this way, and you have product marketing thinking the same, it becomes much easier to align staff and resources.  Product managers and engineers who work on Oyster projects need to be thinking differently than people who are managing the Bread & Butter products.   The challenge for the management team is to keep things moving, you want Oysters to become Pearls or to go away, you need Pearls to move to Bread&Butter, or they may need more time (Oysters).  White elephants need to leave; that takes special skills and support from the organization to accomplish.