Keynote '09 is probably the application where changes are least obvious. In fact, the biggest addition isn't even part of the program itself, but rather one for the iPhone and iPod touch - the aptly named Keynote Remote app.
Don't think I'm complaining, though, because I'm not; Keynote Remote is quite simply brilliant. Rather than acting as a simple dumb trigger between slides, the app enables viewing not only of the current and next slides in landscape mode but also supporting notes for each slide in portrait. This, as with the iTunes Remote application, communicates with your Mac via Wi-Fi, so does require an existing wireless network, but provided you have this it's a great way to present without being beholden to your notebook.
Keynote's other enhancements are largely superficial. Even more themes than previous versions, displayed via an enhanced browser take a fair bit of effort out of creating a slideshow, and once created jazzing it up is as easy as pie.
The new Magic Move transition is my favourite. Where two adjacent slides have the same object on them, say a company logo or a subject heading, in different places Magic Move animates the change from slide to slide. As simple as it sounds, it can create some pretty funky effects such as, as demonstrated at the MacWorld iWork '09 announcement, shuffling a deck of cards. Gratuitously fun? Yes. Useful? Debatably.
3D animated charts are also add some visual stimulation to what could otherwise pose dull subject matter. And, as already mentioned, these can be embedded from Numbers spreadsheets.
Admittedly none of these animation effects will totally compensate for boring subject matter, but if nothing else presentation creators will find their jobs that bit more satisfying and for those working in creative industries the extra flexibility over Office's more mundane appearance will prove particularly appealing.