This is old news from last week, but YouTube has been slowly adding HD-quality videos to it's regular service. Anyone who has been on YouTube in the past couple of weeks has seen that they went to a wide-aspect 16:9 ratio.
Now the service will show videos made in HD at their best trying to keep up with SmugMug's great video services.
Many people feel most web video is "good enough", but the difference in HD video is pretty great. I took this side-by-side comparison of the 2008 Where the hell is Matt video and captured this screen shot, showing the difference in quality between the two versions.
And if you aren't familiar with Where the Hell is Matt, get familiar with it. It's good stuff.