In a recent court case in the U.S. (2004), a judge found in favour of the plantiff who complained that the song they wrote was to similar to one Mariah Carey had co-written. The two songs were One of Those Love Songs" by Seth Swirsky and Warryn Campbell and "Thank got I've found you" by Carey. You can compare the songs.
Using expert opinion in these cases is somewhat difficult, but the plantiff's complaint was upheld on the basis of evidence produced by Schenkerian analysis.
This is a very good example of the use of music IR techniques in plagarism detection.
(h/t: Darrell Conklin)