This thread keeps evolving, so it's time for me to post again. As a Rio de Janeiro resident I have never had any violence at all towards me and none in recent years to any family or friends, a circle of a couple hundred people. That said, there have been attacks fairly close by.

I find walking in Rio perfectly safe day or night, and do so regularly. We live in Jardim Botanico but go to Leblon, Botafogo, Ipanema and Copacabana every week. We sometimes visit friends in Dona Marta, a favela, at night. Friends often dine in favelas. I mostly am not inclined to do so myself, but it is good to be realistic.

Yes there are dangers in Rio and Sao Paulo also. If you behave in an urban conscious way you are quite unlikely to have problems. If you:
1)drink and drive-beware.
2) buy drugs-beware
3) be obviously inebriated walking late at night-beware
4) pick up the readily-available ladies/men of the night-beware
5) flash your money-beware
6) wear much jewelry or obviously expensive clothing- beware
7) wander about in dark deserted streets after dark- beware

Otherwise you're not likely to have many problems.

Don't accept the panic. Just be prudent.