Probably the biggest threat in Ibiza (like many other popular destinations) is by bag snatchers and pickpockets, when at the beach, make sure you always keep your possessions in sight.

Drive carefully!, especially in summer; due to the large numbers of tourists, roads tend to be packed, this means you will naturally come across people speeding and also many inexperienced drivers. If your driving a scooter make sure you use a helmet and keep to the sides of roads.

There is much worry about gas water heaters in overseas resorts following the tragic events in Corfu in 2006.  However, most tourist places in Ibiza have electric water heaters. Some older private apartments may have this type of water heater, but the gas bottle (there is little piped gas on the island) and the water heater itself should both be outside.  check this out before you book.  Some places still use gas bottles for operating gas cookers - this is a completely different kettle of fish but always better if the gas bottle is kept outside.