Read a posting on this board recently in which the poster said he/she had booked a car in Croatia to take to Italy, rather than the other way round, because Western European car hire companies did not like their cars going into Croatia because of theft.
Is it really that bad? Do they mean car theft? Or do they mean theft of belongings from cars during which cars get damaged, vandalised etc? (Presume it's not just theft of belongings from cars with no damage - we might care about that, but why would the car hire co's?)

What has been the experience of travellers on this forum, and what security measures can be taken? (For example, I've read Dubrovnik is a "park & walk" city, but are the parking areas supervised or patrolled?)

The croats are some of the most honest people in Europe. I would be more worried about theft in Italy than Croatia.

I think the poster had his wires crossed.

Sometimes car rental companies don't want you bringing cars outside of the EU states - but its not for any particular reason other than their strange insurance policies.