Youtube is testing a new system called Feather, which would deliver their content much faster. Lower latency and reducing the stream from 391 KB to 52 KB are amongst things to watch for.
Though it doesn't yet work for all video's, you can join here.
This doesn't seem to work with Opera or Firefox at the moment because of interpreting issues of the HTML 5 code using ogg or H264 (youtube using the later). Internet Explorer can't handle it at all, so use Chrome or Safari if you want to test.
Edit: Here's an article of Firefox defending why they only play ogg and no H264
