We had one explode in someone's back yard here in Vienna (Austria) a couple of weeks ago, it felt like an earthquake to people within a certain area. Luckily, no one was hurt, it just left a huge crater. They also come across them frequently when doing construction work for roads - you hear it on the radio that the motorway is closed until the bomb squad arrives. Scary stuff.
In July a WW1 mortar shell was found and detonated in the Presidio of San Francisco...<p><a href="http://www.ktvu.com/news/16764203/detail.html?psp=news&rss=fran" rel="nofollow">http://www.ktvu.com/news/16764203/detail.html?psp=news&r...</a>