TED is a nonprofit organization that holds conferences yearly with speakers in the areas of Technology, Entertainment and Design. The speakers are challenged to give a talk about their lives in about 20 minutes. I found Paula Scher's talk video where she discusses the difference between serious and solemn design. She confesses her hatred of the typeface Helvetica in her twenties and that her best design work was created intuitively out of "serious play" rather than her more informed "solemn" work. She shows slides of her work over her life time and discusses when a project transitioned from serious to solemn. I think that its important to learn everything you can from great designers and these TED talks are the perfect opportunity to do so.
There is also a shorter talk by Stefan Sagmeister where he talks about the things he has learned in his life and another one where he discusses "happy design."
(TED's website videos don't seem to be working on Temple's internet so if they don't work for ya here is the youtube versions.
Scher: Serious play.
Sagmeister: Things I have learned so far.
Sagmeister: Design can make you happy.)