Sorry, no. Theora is better than H.263, which YouTube currently uses for compatibility with older Flash players. This does mean that Chris DiBona was wrong, but Theora is still worse than H.264 (which YouTube uses for all but the lowest quality clips).
Check out the last graph on the page. As they point out, PSNR isn't a 100% unbiased way to compare codecs. However, the graph, made by the theora developers themselves running the bleeding edge encoder on content of their choosing, clearly shows that Theora requires 50% larger files to produce the same PSNR as H.264.
http://web.mit.edu/xiphmont/Public/theora/demo7.html
Check out the last graph on the page. As they point out, PSNR isn't a 100% unbiased way to compare codecs. However, the graph, made by the theora developers themselves running the bleeding edge encoder on content of their choosing, clearly shows that Theora requires 50% larger files to produce the same PSNR as H.264.