I consider myself a power Keynote user, and overwhelmingly prefer the app over PowerPoint (on both the Mac and PC) -- even though though I'm just as well-versed at PowerPoint. Only on rare occasions do I start my presentation workflow in PowerPoint (if the deck is going to be chart-centric, to avoid the limited axis and error bar support in pre-09 versions of Keynote).
While both Keynote and Powerpoint get you from Point A to Point B, it's the "little things," such as alignment guides and better graphics support (i.e., native support for Photoshop PSDs and Illustrator AIs), that make the presentation journey that much more enjoyable and more presentable.
One of these little things is Presenter View. Although PowerPoint has a similar feature (in both Mac and PC versions) it lacks the polish and ease-of-use found in Keynote. Presenter View allows you to look at your slide's notes, and upcoming slides and builds, without your audience's knowledge.
So while your audience sees this:
You see this, full of notes and upcoming builds and slides:
Setting up Presenter View requires several steps. The first step is to display your Keynote presentation on a secondary display, which is accessible via the "slideshow" pane within Keynote's preferences. Secondary display, in most cases, will refer to a projector. So, if your display preferences are set for mirroring, make sure remove the checkmark from it.
Next, within the "presenter display" pane of Keynote's preferences, you'll want to enable "Use alternate display to view presenter information." Most people's "alternate display" will be their MacBook, MacBook Pro, or MacBook Air -- unless, of course, you happen to lug your iMac, Mac mini, or Mac Pro with you to meetings.
Voila, you'll now be one step ahead of your presentation, and appear to be extremely prepared for it as well -- as if you weren't already.
(Note: Black turtleneck, Levi's, and Grey New Balance 993's sold separately.)