project_view.xml

<openerp>
    <data>

        <record id="view_task_search_form" model="ir.ui.view">
            <field name="name">project.task.search.form</field>
            <field name="model">project.task</field>
            <field name="inherit_id" ref="project.view_task_search_form"/>
            <field name="arch" type="xml">
              <field name="user_id" position="after">
                <field name="department_id"/>
              </field>
              <filter name="User" position="after">
                <filter string="Department" name="group_task_department_id" context="{'group_by':'department_id'}"/>
              </filter>
            </field>
        </record>

        <record id="view_task_form2" model="ir.ui.view">
            <field name="name">project.task.department.form</field>
            <field name="model">project.task</field>
            <field name="inherit_id" ref="project.view_task_form2"/>
            <field name="arch" type="xml">
                <field name="categ_ids" position="after">
                  <field name="department_id" />
                </field>
            </field>
        </record>

        <record id="view_task_tree2" model="ir.ui.view">
            <field name="name">project.task.department.tree</field>
            <field name="model">project.task</field>
            <field name="inherit_id" ref="project.view_task_tree2"/>
            <field name="arch" type="xml">
                <field name="user_id" position="after">
                  <field name="department_id"/>
                </field>
            </field>
        </record>

    </data>
</openerp>