I heard about this from an old blog friend, and it is both wonderfully simple and delicious.
Make a normal plain sponge, but keep it in the tin once cooked and allow it to cool.
Mix together a tin of condensed milk, a tin of evaporated milk and a carton of single cream. Prick holes in the cake and pour the milk over the top. You will need to do this in 2 or 3 lots, allowing the milk to soak in. Put it in the fridge over night to let things really get absorbed.
The result is wonderful, and not as sweet and sloppy as you would expect. I guess you could do a similar thing to revive cake that has.gone a bit too dry too.
Give it a try, but not if you are trying o diet!