Seeking in Ogg/Theora/Vorbis files works fine in Firefox. If seeking is broken in other players, it's an issue with their implementation.
This is awesome — finally someone released an implementation that's more reliable than liboggplay instead of just doing the minimum necessary to get basic playback. I guess when you won't support other containers (because noobs would think you supported other codecs (which you refuse to do on ideological grounds)), you have a really strong incentive to make OGG actually work.
Now to get everyone else using your implementation… :)