HI John,
This information wasn't meant to scare you away from Costa Rica, but to advise you that crime does exist. A lot of people think that just because most Ticos are friendly and the country is so natural that no crime exists and they don't take the normal precautions that they would back home. I would also like to point out that the experience your friends had could happen to them at any vacation destination in the world. I worked on a cruise ship for 5 years and visited over 30 different countries an islands. Passengers had their cameras stolen in every port.
Their rental car was broken into - twice, in just one week. And in San Jose, the capital, they were accosted and had their camera stolen.

This is unfortunate, but tourists normally stick out and thieves really can spot them. You have to be very aware of your surroundings, never leave any bags or boxes in the car and watch out for people around you. At the Vatican in Rome, kids used to come out and ask for hand outs on a newspaper. Under the newspaper their friends would steal your wallet.
In summary, Costa Rica could really do a lot more to fight criminals, especially those targeting tourists. But I wouldn't say that crime is any worse that in other countries and shouldn't dissuade anyone from making their home here.