MACHAON  This is a great piece of basic software for adding a voiceover to a very simple presentation. The nice thing about it is that it works in the background whilst you give the presentation directly with keynote, so that you can actually give the lecture and transparently have it create a file with the slide transitions synchronized to your lecture. It also includes a podcast manager for easy upload to sites like .mac etc.

Having said that, video is an essential part of all my presentations (it is the actual data), and profcast doesn't capture any video (with the current version 2.1.3) so, frustratingly, profcast is nowhere near as useful as it could be. I can still create separate links on my website for the videos, but we've lost the voice synchronization that was the point of getting profcast in the first place. Hope they fix this soon.  
(Version 2.1.3)