I just bought the Apple TV. Can I stream Amazon from my MacBook to my TV?
If your Mac supports Airplay mirroring, then yes you can mirror your mac's screen to your Apple TV, and anything on that screen will appear on your TV. So you could just start streaming Amazon Instant Streaming on your mac, and mirror the screen to your ATV.
But to support airplay mirroring your mac needs to be:
iMac (Mid 2011 or newer)
Mac mini (Mid 2011 or newer)
MacBook Air (Mid 2011 or newer)
MacBook Pro (Early 2011 or newer)
http://support.apple.com/kb/ht5404
If your mac doesn't support Airplay Mirroring, you may still be able to do it via an application like AirParrot, which has more lenient requirements.
http://www.airsquirrels.com/airparrot/
Regarding iOS devices: Yes you can definitely airplay Amazon Instant Streaming shows/movies from the Amazon Instant Video app to your Apple TV. I've done it multiple times within the last month.
Either way, the only downside is that it tasks your mac or your iOS device. But at the moment these are the only ways you can get Amazon Instant Streaming via Apple TV.