Yes, this is how Move Network's streaming works, how Apple's streaming works, and Adobe just announced official support for streaming this way last week[1] (edit: oh and microsoft buit it into iis too).
What they do is parallel-encode their video feed to many different bitrates, then as the client is keeping up or not keeping up with the incoming chunks they move up or down the scale of which chunks to send. The best part is, it works via existing http cdn's like level3 and akamai, so just about anybody can stream live video this way to as many people on the internet as they can get to watch it for the already commodity cost of cdn bandwidth.
This is a common misconception. In fact, HTTP Live Streaming as proposed by Apple has nothing to do with chunked encoding. The former splits the video into multiple "chunk" files, using an m3u file as a playlist. Stream variants are supported by having multiple sets of video and m3u files, but dynamically switching between them based on bandwidth is left to the client.
What they do is parallel-encode their video feed to many different bitrates, then as the client is keeping up or not keeping up with the incoming chunks they move up or down the scale of which chunks to send. The best part is, it works via existing http cdn's like level3 and akamai, so just about anybody can stream live video this way to as many people on the internet as they can get to watch it for the already commodity cost of cdn bandwidth.
[1] - http://arstechnica.com/apple/news/2011/04/adobe-throws-in-to...