There has been a nice discussion H.264-in- vs plugin APIs on the WhatWG list.
This lead to Greg Maxwell posting about his experience with the quality of Ogg Theora with real world examples, and Chris Blizzard linked it up with 35 days offering the following lead in:

The codecs being discussed are the same ones we’ll be including in Firefox 3.5 and are also the same codecs that Mozilla, Wikipedia and others have been investing in.
Recent developer nightlies of Google Chrome support these codecs and a future version of Opera will also support them. Theora and Vorbis also work in Safari if you install the Xiph Qt component. We’re quickly reaching the point where all modern browsers support these open codecs with full support for the video tag.
You’ll note that Greg’s post doesn’t have the tone of a marketing document - it’s not meant to. Nor is this a comparison against HD-sized, high-bitrate video. Instead it’s an attempt to give an honest comparison of how the open codecs fare against commonly-used formats and sizes used on the world’s largest video site. I think you’ll agree with Greg’s conclusions at the bottom of the document, especially with audio where Vorbis really shines.

There is also a discussion on how Quicktime doesn't seem to have a nice way to auto-download codecs these days, and the Xiph Qt folks haven't had an easy time getting someone at Apple to work with them. Hopefully that will change with Quicktime X.
Another hope, is that YouTube will push even harder and test out more and more with open codecs (they did the one HTML5 demo at Google I/O, but that is just a demo). If Google puts its muscle behind the standard, then a lot of the video out there would turn open pretty quickly. That being said, Google is a business, and there are lots of factors into making that happen....