search - I have always used query strings, since it will return a subset of some resource.
deleting songs from a playlist - the way it is worded makes you think you should use DELETE but if I said, deleting words from a blog post you wouldn't think of using DELETE. Use PUT for this operation.
multidimensional stats queries - this one is hard if you don't create some umbrella resource that contains the possible resources that may be returned (and most likely I would just make it multiple calls instead of one)
Comments
search - I have always used query strings, since it will return a subset of some resource.
deleting songs from a playlist - the way it is worded makes you think you should use DELETE but if I said, deleting words from a blog post you wouldn't think of using DELETE. Use PUT for this operation.
multidimensional stats queries - this one is hard if you don't create some umbrella resource that contains the possible resources that may be returned (and most likely I would just make it multiple calls instead of one)