My experience has always been that straw on top of soil encourages slugs underneath by offering shelter and moisture. But in the dry summer of 2011 (remember that one?!) a straw mulch worked well and potatoes were barely eaten as slugs were breeding much less, and it was after a frosty winter too when slugs took a hit, unlike this winter when their numbers are still high.
If you are on sandy soil it is probably worthwhile but otherwise I would use straw in the compost heap or, if you have a lot, and if you have space, I would simply stack it to finish rotting into dark compost, then spread it inb the autumn.