Here is a big list of MP3 patents, all but four have expired:
http://www.tunequest.org/a-big-list-of-mp3-patents/20070226/
The last four might not affect an ordinary MP3 decoder, and the last four expire by December this year, so either way things are going to be “out of the woods” soon.
Does anyone know any good C++ MP3 decoders?