I was telling a friend about salt vs slug and the effects. He said when he was young, his Grandmother use to put a piepan with a little beer in it in the garden at night, in the morning they would be in the piepan... whats the connection? And what happens to them?
Pickle's right about hedgehogs. Slugs or not, they'll just go for the beer. If you put out a slug beer-trap, please make sure it's covered in such a way that hedgehogs can't get access to the beer.
They've enough trouble crossing roads safely without being drunk too!
The problem with beer traps, as has already been pointed out, they attract slugs, but not only the slugs in your garden, but your neighbours, and his neighbours gardens too, in fact, they come from quite a large area to siip your amber nectar.