Google acquired On2 last year, the company behind VP3, the technology that would eventually become Theora. On2 claimed that VP8 would be vastly superior to H264, so when Google acquired the company, people started hoping that they would open source VP8, delivering a patent-free open source codec that would surpass H264 in every way. It's only a rumour at this point, and I can't vouch for the site in any way. We'll have to see how this unravels.
The rumour also states that Firefox will include support for the codec, instantly covering most of the HTML5-capable browsers available. Opera will surely follow soon (they prefer open standards too), so the question will be what Apple and Microsoft will do.
My hope is that alongside the announcement of the open source codec, Google will announce that the HTML5 version of YouTube will use the new codec, forgoing H264 altogether. Browsers not capable of VP8 would then be served the Flash version, which would hopefully force Microsoft and Apple into adopting VP8 as well. It would be a perfect way for Google to slap Apple in the face for suing HTC.
Time will tell. Everything that helps to prevent the prospect of a web shackled to yet another proprietary and patented-up-the-wazzoo technology is welcome, and Google holds the trump card here: YouTube.