in the description of the ORDER BY clause (http://www.postgresql.org/docs/current/static/sql-select.html#SQL-ORDERBY) it says:
"Character-string data is sorted according to the locale-specific collation order that was established when the database was created."
Which is no longer true with 9.1 as it is possible to define the collation on a per-column basis or as part of the ORDER BY clause.
I think a link to the collation chapter and a description on the "precedence" of the definitions should be added to that part.
Regards
Thomas