The visa to Brazil can be a hassle. GRU isn't too bad of an airport, but the walk from the plane to customs always seems like it's about a mile long. Coming back a few days ago, the line for international departure screening seemed like it was a kilometer long. (Maybe only 300 meters, though.)

The ATM's I saw all wanted to charge $R8 for withdrawals.

I stuck to using one credit card for all purchases, and have had no problems. Used it almost everywhere from the supermarket, to small restaurants, to big hotels. If I'm ever really leery, I'll take a card with no balance, and use it exclusively. Easier to track criminal charges.