To give a different perspective - I have spent an average of about 4 weeks a year in Sao Paulo for the last 4-5 years staying in places as varied as the Intercontinental Hotel and the Augusta Plaza (about $US30/night) in the middle of the red-light district. I am currently in Sao Paulo.

In all this time spent here I have never had anything bad happen to me. I walk the streets at 3am without a lot of concern. I have but wouldn't advise doing this around the Republica area but apart from that if you stick to the main streets and are aware of whats going on around you, my experience is you are unlikely to come to grief.

No doubt lots of forrific things happen in Sao Paulo and if you watch the local news broadcasts you'd get on the next plane out (same goes for Rio) but the truth is, its unlikely to touch you.

If its your first trip to Brasil, I don't know that I would spend it all in Sao Paulo. Apart from the great nightlife there isn't a lot to offer the tourist. Spending Thurs-Sunday in Sao Paulo and going to Rio midweek where there is plenty to occupy your days would be my suggestion.