buddy wants to go to Mexico City and Guanajuato for NYE. is there any reason to be a little skiddish about safety down there?
There are certainly dangerous areas in Mexico City. So long as you stick to the tourist areas you should be fine, but be very aware of your surroundings and don't venture off the reservation. Pickpocketing is pretty bad I think, so plan accordingly. No idea on Guanajuato.
Also, in Mexico City the water is not purified and safe to drink as it is in many of the tourist areas. This applies to anything made or handled with it (ice, salads, unpeeled fruit, etc.).