Success or failure?

On the day Tony Blair left power Welsh Labour and Plaid Cymru have reached an agreement in principle to create a coalition government (details of deal here pdf file). If endorsed at party conventions this will mean every nationalist party in the United Kindgom are part of the devolved executives. Should this be viewed as success for Tony Blair’s devolutionary reforms now that the Union’s structures are operated by its opponents or the fulfilment of critics worst fears that devolution would lead to dissolution?