Podcasting has gotten a whole lot easier with the advent of GarageBand 3. Previously I used Audio Hijack Pro, but GarageBand has been updated with features designed specifically for podcasters.
For the PowerPage Podcast I use two low cost microphones adapted from XLR down to quarter-inch which are plugged into a Miglia HarmonyAudio box which is connected via Firewire to my MacBook Pro. GarageBand picks up both of the input channels (set them to mono, btw) and all you have to do is press the record button.
One of the best podcasting features in GarageBand is the ability to add chapter markers by simply dragging and dropping artwork to the Podcast track. GarageBand adds a marker and allows you to give each chapter a name and a URL if there's a Web site that you want to reference. GarageBand also lets you add Episode information to a podcast like the title, artist and a description.
GarageBand is far from perfect, however. It lacks a way to edit the RSS feed that tells the world that you've updated your podcast and that a new episode is available to download. Currently you have to edit the XML file manually or use a tool like Reinvented Software's excellent Feeder (US$30) application to do this. You can export your finished Podcast to either iTunes or iWeb from the Share menu but only in AAC format, making it only playable on the iPod. The Export > Audio Podcast Settings in the GarageBand preferences could use some additional choices or (ideally) a custom option allowing you to chose your own settings and file formats like MP3 or OGG.
And although GarageBand claims to be able to record an interview over iChat, I've had nothing but problems with it when used in this manner. Most of the time iChat will not connect saying that the other party cancelled the connection (when they didn't). Other times GarageBand doesn't recognize that I'm in an iChat conference and won't let me record it. I have only successfully recorded one iChat conference in GarageBand out of about ten attempts. Also, since it's an Apple product recording a Skype or Gizmo call isn't an option.
So while it has some great additions for podcasters, there is still plenty of room in GarageBand for improvement.