El Portrero Chico is totally awesome. Was there in Jan 08 and it was fine. The locals are super friendly and even the Americanos are okay. Spent 10 days in Mexico City and felt totally safe the whole time. On the other hand turning up at Cuzco bus station at 3.00am was not much fun and not very safe. Having just spent a year in Vancouver before going to South America I can tell you I at no time felt more scared in South America than I did walking down Hasting St, Vancouver at sunset. If you want to see the frontline of the drug problem this is it. Anyway off topic.
Bouldering on the altiplano in Bolivia at 4500m is supposed to be amazing. Can't remember the name but you will find it on internet.