I heard Chris Pirillo interviewing Michael Robertson of the Gizmo Project, on the Chris Pirillo podcast. It's a great interview, and provides a more in depth understanding of how Gizmo is different to Skype. Interesting points are that Gizmo is not peer to peer, and therefore will not eat up CPU bandwidth when you are not making a call. Another feature that I didn't mention in my first post, is that Gizmo allows free voicemail, whereas for Skype, you have to pay for this. They are also in the process of adding sound effect capability so that while recording a podcast, you can add in sound effects.