There's an excellent editorial on PM Forum about the increasing view of PMOs as "unnecessary bureaucracy" by many senior managers. Unfortunately, many PMOs have created this situation for themselves.
The trick is to focus on streamlining schedules and reducing overhead costs, but in reality the "lets' make our process fit the most complex project we can imagine" approach often results in the reverse---according to the article---as people on normal size projects don't know which items are optional and which are mandatory.
If done right, a PMO can be an excellent way to institute repeatable lean processes, upskill the organization, and remove barriers for project teams. If done wrong, it can appear as a bureacratic burden on the organization.
This editorial is well worth reading for those starting a PMO and looking to avoid being a statistic ...
PMFORUM, Connecting the World of Project Management - Editorials