@flaconspatrol I’m going this year and am staying in central Barcelona, although did consider Mataro, a few miles up the coast. Check out the Circuit de Catalunya website (english vesrsion) for useful info and a schedule for 2011 GP a this gives you an idea of what time to arrive each day. For getting there, i’d use the train from Barcelona to Montmelo (every 30 mins) and then a short walk, 25mins, to the circuit. Have an idea of where you want to be as there are various entrances rather than just going with all the crowds to the main entrance.
For sites in Barcelona, well there are loads, just be careful in tourist areas with your bags and wallet. Try to visit the Olympic Park at Montjuic which is a previous location of the Spanish Grand Prix, you’ll be amazed that they used to race along those tree lined streets.