It is already possible to Airplay iPhone and iPad screens on your Apple TV, but font issues still complicate the transfer of presentation files from computers to mobile devices. Currently, Airplay mirroring is not supported for Macs. The next version of Mac OSX will allow Airplay mirroring of Mac screens wirelessly to your Apple TV.
If you cannot wait, well, there is an app for that. Airparrot enables sending your Mac screen wirelessly to you Apple TV ($10). The app has many customization features, allowing you to adjust the performance/quality trade off and select which screens you want to transfer, or even which apps. You can switch off the cursor.
Still we are not yet living in the world of 1-click Airplaying of video. Television screens have a lower resolution than computer screens. So before using the app, you need to downgrade your Mac display to 1280x800, the closest to my Apple TV 1280x720 resolution. After that some fiddling with the screen remote to get the right aspect ratio. The resulting screen sharpness is OK, but not the pin-sharp feel you get from watching an HD movie. It is perfectly fine to play presentation slides (which are often 1024x768), but less than optimal for other applications.
Soon we will all laugh about this. Until then, a struggle to get rid of the cables.