Use your Mac with AirPlay using AirPlayer
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Erica Sudan has made a nice little utility called AirPlayer (look for the download link in the list at the bottom of the page) that makes it dead simple to use your Mac as an AirPlay destination device. Sort of like turning your Mac into a TV with an AppleTV attached.
I just used the YouTube application on my iPad and played the video back on my Mac using this utility and it works just fine. Simple too.