You can talk to people who've been there, but each country is pretty different and there are major differences within countries, as well.
As far as the violence goes, it tends to be cyclical. Certainly in parts of Columbia FARC activity is still a major issue, and Venezuela is bad for petty crime and assaults. You get the occasional Shining Path incident in Peru, but it's very low-level. Bolivia has regular strikes that bring the riot police out in La Paz, but the rest of the country seemed perfectly safe. Never had a problem in Argentina, or heard of anyone having problems in Chile, Uruguay, or Paraguay. Brazil is mostly kosher, but I heard of a few people getting robbed, or more likely picking up a girl from a club and getting mugged after.
But seriously, do go down if you get a chance. I had a blast there.
As far as the violence goes, it tends to be cyclical. Certainly in parts of Columbia FARC activity is still a major issue, and Venezuela is bad for petty crime and assaults. You get the occasional Shining Path incident in Peru, but it's very low-level. Bolivia has regular strikes that bring the riot police out in La Paz, but the rest of the country seemed perfectly safe. Never had a problem in Argentina, or heard of anyone having problems in Chile, Uruguay, or Paraguay. Brazil is mostly kosher, but I heard of a few people getting robbed, or more likely picking up a girl from a club and getting mugged after.
But seriously, do go down if you get a chance. I had a blast there.