We've never had our sails professionally washed, partly to save money, and partly because we believe the laundering process is quite hard on them, and creates unnecessary wear. What we like to do is give the sails a really thorough hosing down with fresh water on the boat and hoist them up to dry (in situ) on a quiet day in the marina (or take the boat out for a gently sail while they dry), before we take them off. This gets the salt out, which, as Scotty describes, otherwise prevents them from ever drying properly.
We always used to wash our spinnakers in the bath, too, but the current ones are too big. So now we rinse them with a hosepipe and hoist them to the masthead, loosely tied in a tube, to drain. It is suprising how quickly they dry, even on a cold day. We never hoist the spinnaker to dry and leave it flapping free, as some people do, because of the unnecessary wear (and noise!) that causes.
Like David, we use Dettox to tackle mould spots on sails, headlinings, etc.
Sails are so expensive that I'm astonished how many people don't make the effort to rinse them and take them off the boat before laying up for the winter. You see so many boats sitting in their cradles with their mainsails still on the boom, and the genoa still wound round the forestay. The sails are bound to deteriorate from exposure to the worst weather, atmospheric pollution etc.
