Roberto is asking a very difficult question: is OGG/Theora a standard, after all? Since it is not documented in anything else but the source code, and the code is distributed under BSD license, what will make sure that nobody will start predatory practices on the format?
I understand Richard’s request though, based on practical terms as usual: there are no other formats for audio/video that aren’t encumbered by nasty patents.
Is OGG a standard? Probably not. Is it an open unencumbered format? I think so. Will my data be safe for future use? This is the most difficult question to answer: one can say that since the code is out there you can always write the decoder. But real life is more complex than that.