I use podcasts to learn while I work. I listen to design talks, keynotes, interviews and news from science, culture and some entertainment. Especially during the tasks every designer can do without thinking (photo retouching, filling in content, corrections) are the ideal activities to up your game by staying in touch with the latest developments. Even though graphic and web design are visual media, the most important part in my opinion about design is not visual - the mindset and the different approaches behind design solutions. In the old days it was really difficult to get the inside view of designers because not many had the opportunity to publish books or discuss their point of view in a magazine. Design Blogs fill this space a little bit but mostly podcasts can give you the opportunity to hear what designers think in their own words.
To give you a further starting point for the design podcasts I listen I publish here my Subscription list from Google Reader (if you want you can even subscribe to it) - this list will update itself automatically.
Photo by Melvin Gaal (Mindsharing.eu)