It seems the right to mix audio clips is being defended in congress
http://splashcastmedia.com/us-rep-defends-mixtapes-and-mashups-on-floor-of-congressPennsylvania’s Democratic Representative Mike Doyle made a moving statement on the congressional floor last week in defense of music mashups and mix tapes. Doyle discussed remix artist Girl Talk, arrested mix tape maker DJ Drama and even Paul McCartney’s admission that he used a bass line right out of a Chuck Berry song. The statement was made as part of the very important (and frightening) congressional debates about the future of radio.
After seeing some of those who mix being sued for various minor audio infractions its hard to decide whether it really is legal to mix mashup tapes etc as while on paper its legal in reality the RIAA dragon is likely to come visiting with more jumped up and speculative claims.