I stopped using the organic slug pellets as having noticed that they disapperared at far too fast a rate for slugs alone I started keeping a watch. Squirrels, small birds, large birds (including a particularly stupid pheasant), and frogs all seemed to think they were an interesting snack. They are not supposed to harm other animals but they can't be good for them!
In the garden at large I don't worry however in the veg patch it's another matter. I find the only thing that really has an impact is manual collection. I pop them into a pot of neat vinegar. Kills them in seconds (helps the concience) and there are no nasty smells to worry about!
Marigolds do seem to act as a draw thus making the blighters easier to collect.
We may win the battle but you can count on it that they will win the war!