I'm in the same boat. Started a web design and development firm 12 years ago, became one of the first Rails shops, and now I'm (finally) doing a product company.

About 6 months ago, I had an idea for a product, designed it, and put together the final team in the last 6 weeks. I've leveraged old contacts for customer development, and getting the demo done. Now we're pitching some of the largest VCs and angels in the world. Exhilarating stuff.

Maybe I just needed to find out myself, but there's a whole new energy level for myself, and those around me. I think the feeling of satisfaction has less to do with dealing with insane clients, and more to do with creating something that is my baby, rather than someone else's, though.