I think the prayer 'Thy will be done' isn't about abdicating responsibility, but a reminder to ourselves that there is a higher will for our lives, that if we truly want to live, we need to conform ourselves with it.

It's so easy to go about doing our own thing, becoming full of our own opinions, plans, and desires, but even simply praying 'thy will be done' opens us up to giving God, Source, Spirit (whatever name you want to use) a chance to get through to us and nudge us along the right path - to flow with the spirit so to speak.

I think we do have free will, but I also believe that we only truly live in that free will, when we're merging it with God's will. For it's when we're being completely controlled by God that we are in complete freedom.