It's also important to keep in mind that if you're primarily watching video streamed from the iTunes Store your actual viewing experience shouldn't be all that bad regardless of throttling as the video buffers into the 8GB of on-board memory on the Apple TV (you can't manage this -- it's merely used as a buffer). For iTunes Store content, the Apple TV tries to load enough of this video into memory before starting to ensure that you get a smooth, uninterrupted viewing experience. Therefore, what you're more likely to encounter is a longer period of time before you can start watching something, but few to no interruptions during viewing.
Note that this can still sometimes be a problem if you have a very variable Internet connection, or if your ISP performs dynamic per-stream throttling -- that is starts the stream at full speed and then throttles it significantly after a few minutes. In this case, the Apple TV starts out thinking it has a lot of bandwidth, so it buffers a couple of minutes of the video and starts playback, assuming that it can continue to buffer the video in the background at the same speed in order to keep up. However, if the ISP suddenly drops the bandwidth dramatically for that particular connection, the Apple TV can't keep up and you'll get pauses and delays once you reach the end of the buffer. In this case, the only way to avoid the issue is to pause the video when playback begins and not actually start watching it until you're sure enough of the buffer has filled up -- which you'll be able to see in the form of a white progress bar overlaid on the standard playback position bar.
Note also that this buffering doesn't apply to services like Netflix. In this case, you'll simply get reduced video quality if you have insufficient bandwidth, and may even sometimes encounter pauses in playback, although Netflix and the Apple TV do their best to avoid this by using a lower-quality stream. Similarly, navigating in a Netflix stream (e.g. skip forward/back) can be a pain due to the lack of buffering even on a higher-speed Internet connection as it has to adjust the stream rather than merely the buffer. I've found this issue alone annoying enough that I've actually chosen to actually purchase some of my favourite shows from iTunes rather than relying on Netflix streaming for them.
Lastly, none of these issues really apply if you're streaming content from your own iTunes library on your home network. Buffering still occurs from your computer to improve performance, but any properly-configured Wi-Fi network should have no problem keeping up even with 1080p streams unless you're having other network performance or stability issues.