According to: http://my.opera.com/core/blog/2009/12/31/re-introducing-video, Opera 10.5 (still in alpha/beta) supports Vorbis and PCM Wav for audio. I don't believe 10.10 actually supports the audio tag.
Safari would support Vorbis (and Theora on the video side) if Apple ever bothered to include support for Xiph's codecs in the QuickTime framework (you can add it manually, of course, with XiphQT, but you obviously can't count on it for web dev purposes).
In any case, Vorbis clearly has the most coverage (Chrome has more of the market than Safari now, Opera is about half of Safari, and obviously FF is huge), and it doesn't really have the strong opposition that Theora has. I could actually see Vorbis support in Safari happening in the near future, unlike Theora.