We found one thing a bit ironic and that was that the app wasn't free like the iTunes and Apple TV remote application. Especially when you have already paid $79 for iWork 09. Sometimes we just don't know if we'll ever understand Apple's logic behind these decisions.
The app lets you control your Keynote slide presentation that you present from our Apple computer using your iPhone or iPod Touch. Swiping advances or returns you to the previous slide. While in portrait mode you can view the presenter notes on your handheld device's display.
In landscape mode, you can preview the next slide in your presentation. All of this is accomplished over your local Wi-Fi network which is great since you can be anywhere in the room and not dependent on an infrared beam while communicating with your computer.
We found Keynote Remote to be useful, but it was a bit slow in responding to our desire to flip back and forth between slides. You also could not flip the iPhone and have the iPhone display the portrait or landscape remote modes based on how you held the phone. Instead, you had to manually either mode using the Settings page. We found that to be our biggest complaint about the app, but not necessarily a show stopper.
Linking the Keynote Remote app over Wi-Fi is exactly like linking your AppleTV to iTunes and subsequently your iPhone or iPod Touch using a four digit passcode generated by Keynote.
You can download a 30-day trial version of iWork 09 for your Mac here.