Two new PhD theses have been added to the list of MIR related PhDs recently.
Not too long ago Rui Pedro Paiva announced his completed thesis on the music-ir mailing list. The title of this thesis is "Melody Detection in Polyphonic Audio" written at the University of Coimbra in Portugal. One of his conclusions is that most of the research problems involved in melody detection are complex and still open. So I hope we will see many more PhDs on this topic.
The second PhD added to the list was written by Katsuhiko Kaji from Nagoya University, Japan. (Thanks to Masataka for pointing this out to me!) He wrote a thesis in Japanese with the English title: "A Study on a Universal Platform for Digital Content Annotation and its Application to Music Information Processing". I've seen some work on annotation in the MIR research community, but I don't remember seeing anyone trying to figure out a framework that can be applied to multimedia in general (including text, video, music and so on). If you're interested check the abstract and I'm sure Katsuhiko will be happy to answer any questions you might have.
There are at least two more PhDs from Japan that I hope to add to the list soon. If you know anyone that is about to finish, or has already finished their PhD related to MIR, please let me know.