In general, multimedia is one of the areas that Linux has some catching up to do. Many vendors and developers can't be bothered to support Linux properly, so rudimentary things like Flash above version 7 and Windows Media files cause problems on Linux workstations.
As far as podcatchers go, there are a handful on the market and while most of them are pretty effective, the nice stable GUI ones are few and far between. has had podcast support for a while now, and has been extended by some developers to put a GUI on it. The newest entry into the Linux podcatching space is Penguin TV. Version 2.0 has just been released.
PenguinTV is not just another RSS feed reader. It is designed from the ground up to work seamlessly with podcasts and video blogs, allowing you to easily enjoy the audio, music, and video published around the web in RSS format.
I am downloading it now and will report back on how it fares.