Do you ask your client's permission before using your designs in your personal portfolio?

I am sure this is a topic that will spawn some good discussion.
I personally do not ask, nor do I think we should have to. If the need ever arose where a client wanted me to exclude certain work from my portfolio, I think it would warrant a further cost in the development.

I realize displaying work without express permission probably could land me in hot water, but I perhaps take my work a little more personal and not just as a simple 'product' I hand over to the client upon completion.

Thoughts?