Last week-end I finally got around to lining my strawberry bed with plastic lawn edging to keep in moisture. Concrete is porous and the retaining wall bricks just seemed to suck moisture right out of the soil. I think the strawberries will be extra happy this year!
The other problem with a raised bed, especially lined with concrete or stone, is that it can get very hot if it is in a sunny spot and/or if the bed is not very big. So if you plan to build a raised bed with concrete, brick or stone, my advice is go big or go home!
For a bigger bed, pond liner would make a good waterproof lining.