Niti Bhan's got a very short, very concise, and very clear post on what the heck design is, and what value it brings. If you've got a client, or an organization, or a parent, or a student, or anyone who just wants this enterprise boiled down for them in email-able form, here's the link. Read the whole thing for sure, but here's a paragraph on "design thinking":
Design thinking in business takes this problem solving aspect one step further. Now the tools and techniques from the field of design such as ethnographic research, rapid prototyping and conceptual brainstorming integrate with the pragmatic business frameworks of strategy, analysis and metrics to create and provide roadmaps for business innovation and competitive advantage. In this context, design has evolved away from traditional form giving to becoming an integral part of corporate strategy.