Use crm.lead instead of a the crm.opportunity.report object for
reporting. This allows to show more fields (e.g. tags_ids). The only
field not accessible in the report is #activities, but there is a
deicated report dedicated to activities.
Improved the default search. Example: when reporting on leads, you want
leads+opps by creation date (and not only leads) as an opportunity has
been a lead created too.