While working on Pushtape , an open source Drupal distribution for musicians, the issue of importing/exporting discographies came about. I've been warming up to the idea of using YAML  as a method of defining discographies. I wrote more about my reasoning over here , and I posted a quick example discography.yaml implementation on github. 
Any feedback or comments regarding the idea of using YAML for discography applications is appreciated!
I think all work of this kind helps push open music forward. It's cool
that your basic strategy is Drupal-oriented.
Is it critical that the document be YAML, or are XML and JSON
equivalent? I wonder if it's necessary for your semantics to travel
with YAML syntax.
You might be interested in comparing elements in Discography.yaml to
other formats with an eye towards sharing. EG Dublin Core uses "Title"
instead of "title", XSPF uses "title", Music Ontology imports Dublin
Core as a name space and uses "dc:title" (lowercase?!).
A sample document is good for teaching people how to use the format.
Writing up the field definitions is helpful for those writing parsers.
Defining the ordinality of an element is helpful for figuring out
whether a document is usable. (e.g. 0 or 1, 0 or more, 1 only, 1 or
more). The MUST/MAY/SHALL thing is very helpful for parser authors.
What's the format of the release-date? Date parsing can be a hassle.
If you state a well known format with existing libraries you will
allow people to use libraries.
Hope this is the kind of feedback you were looking for.
> You might be interested in comparing elements in Discography.yaml to
> other formats with an eye towards sharing. EG Dublin Core uses "Title"
> instead of "title", XSPF uses "title", Music Ontology imports Dublin
> Core as a name space and uses "dc:title" (lowercase?!).