Keynote is part of iLife http://www.apple.com/iwork/keynote/. It is Apple’s equivalent of PowerPoint and it is awesome. I do all my professional lectures on it (Al Gore made the movie Inconvenient Truth on Keynote). Great transitions and sharp themes. People in the audience are always asking me “how did you do that” because the program just works. However, you could do the same thing in Office for Mac or whatever program you have. The difference is that the Apple remote control actually advances slides and plays videos in Keynote from across the room and allows you to walk around and interact with the audience.
One of my favorite features is the Auto Alpha which allows you remove picture backgrounds and make them “blend” in with the talk.