Use Case "XMP": Experiences and Exemplars
from XML Query Use Cases.

Source: http://www.w3.org/TR/xquery-use-cases/#xmp

Q1 - List books published by Addison-Wesley after 1991,
     including their year and title.
Q2 - Create a flat list of all the title-author pairs,
     with each pair enclosed in a "result" element.
Q3 - For each book in the bibliography, list the title and
     authors, grouped inside a "result" element.
Q4 - For each author in the bibliography, list the author's
     name and the titles of all books by that author,
     grouped inside a "result" element.
Q5 - For each book found at both bstore1.example.com and
     bstore2.example.com, list the title of the book and
     its price from each source.
Q6 - For each book that has at least one author, list the
     title and first two authors, and an empty "et-al"
     element if the book has additional authors.
Q7 - List the titles and years of all books published
     by Addison-Wesley after 1991, in alphabetic order.
Q8 - Find books in which the name of some element ends
     with the string "or" and the same element contains
     the string "Suciu" somewhere in its content.
     For each such book, return the title and the qualifying element.
Q9 - In the document "books.xml", find all section or chapter
     titles that contain the word "XML", regardless of the
     level of nesting.
Q10 - In the document "prices.xml", find the minimum price
      for each book, in the form of a "minprice" element
      with the book title as its title attribute.
Q11 - For each book with an author, return the book with
      its title and authors. For each book with an editor,
      return a reference with the book title and the editor's affiliation.
Q12 - Find pairs of books that have different titles but
      the same set of authors (possibly in a different order).

magic/xml solutions more or less follow XQuery solutions,
with significant changes only where naive translation
would result in very cumbersome code.