I like (love ?) Keynote because it
- is a simple to use presentation software,
- is vector based (when zooming it just looks gorgeous)
- exports to powerpoint
If I could remove that last argument, I would, but the fact is that, as a consultant, the final document is almost always expected to be a powerpoint document. Don't ask me why, it is just so. I am fighting against it but I did not win the battle so far ...