I spent 6 months in Brasil last year, and the bulk of my time was in Recife (north east, on the coast). I rented an apartment in Boa Viagem with another girl, and we really enjoyed the beach scene of the neighborhood, although most of out party times were spent in Recife Antigo (downtown, basically). There are a lot of clubs geared towards younger people (UK Pub being one of our favorites), but I absolutely loved sitting in the street, drinking beer, and listening to local samba. There are plenty of street vendors who have cheap alcohol and great food, and watching a huge crowd of Brasilians dance and sing the words to their favorite songs was a wonderful, authentic experience.
I also had the opportunity to visit Rio De Janeiro towards the end of the 6 months, and I absolutely fell in love with the city. This is one place where I suggest doing all the "tourist" activities. You will find that even the locals enjoy going up to Pao de Acucar and watching the sunset. Rio has such captivatingly beautiful scenery that it would be a shame not to see O Cristo Redentor ("The Christ Statue") while you are there. Also, visit Corcovado and go to the Lapa street party. I stayed in a hostel (Mellow Yellow) by myself and found Rio to be surprisingly safe; however, I knew the language and I made local friends almost immediately when I was there. The English folks that were in my hostel stayed together in a big group at the Lapa street party and got robbed the first night. A word to the wise: Learn some of the language, don't stay in a big group, don't be drunk and loud and draw attention to yourself. Just try to talk to the locals and observe. And always watch out for "innocent" kids!
While in Rio, I made the transfer to Ilha Grande for a few days. It cost me a pretty penny to get there, but it was totally worth it! I stayed at Che Lagarto hostel and just enjoyed the amazing, remote scenery (this is where "The Blue Lagoon" was filmed). I would suggest either making the 6 mile hike over the mountain to Lopes Mendes beach, or paying for a boat tour of the islands pristine beaches. I unfortunately had a nasty cold the entire time I was there, so I wasn't up for the hike, but I did take a "party boat" tour of the islands beaches. Somehow I managed to stay relatively sober while all the English kids were getting pissed out of their minds. This proved to be a good decision, because while they were all sloppily making out, I was enjoying the most epic sunset swim EVER. It is a moment that is burned in my memory. So don't waste a tour by being sloppy drunk! There are no ATM's on Ilha Grande, so bring plenty of cash, and, if you can, bring some food and booze for yourself- it can be expensive to eat/drink in the hostels or restaurants on the island.
I hope this is helpful for anyone traveling to Brazil! I certainly fell in love while I was there. Just remember to be polite and definitely learn some Portuguese...it's not that hard!