Re: where is pg_stat_activity (and others) in the documentation?

You can find out exactly what you're waiting for by correlating this to the pg_locks table.
  Grab the 'procpid' of your waiting query and run:
  select * from pg_locks where pid=<thepid> and granted='f';
  Notice, in the pg_locks table, the logic works slightly different... if you're 'waiting' (pg_stat_activity), then you haven't been 'granted' (pg_locks).

As far as documentation: http://www.postgresql.org/docs/current/static/monitoring-stats.html