I've notice some error in the XML example of the Doctrine ORM manual, section 6.
There is often:
<join-column="user_id" referenced-column-name="id" />
The correct tag should be:
<join-column name="user_id" referenced-column-name="id" />
Also, in the many-to-many bidirectional example is missing the targer-entity tag:
<many-to-many field="groups" inversed-by="users">
<many-to-many field="groups" target-entity="Group" inversed-by="users">
I also think that the differents values could be better explained.
Hope this will help...