We visited Barcelona during the last holiday break. On the way back home, our flights were cancelled twice and we were stuck there for 2 extra days. The airline staff in Barcelona told us (as required by law) that we were covered by EU regulation 261 that provides protection for travelers who are affected by long delays and cancellations. We filed the necessary paperwork with American airlines and received 600 euros per person for each cancelled flight. So, basically, we had free travel to Barcelona on this trip. Well… it wasn’t really free; we paid for it by 2 wasted days at airport hotels.
This protection is applicable to all flights originating or ending in an EU country. So, if you are delayed by more than 4 hours on your trip to Europe, make sure you submit a claim under EU 261.