We booked through Habitat on our trip to Barcelona in Summer 2010. We stayed in one of their Born apartments. The apartment was a little tough to get to, as it was on a side road and the taxi couldn’t get to it, but the location was fantastic, in the heart of El Born.
Their representative met us promptly and walked us through the details (cash only,up front) and when we called the next morning because our AC wasn’t working, they promptly had it serviced. They were also able to book our cab to the airport. They also provided us with a baby cot and high chair.
I was a little disappointed with the quality of the apartment – it was a bit run-down, with the paint chipping in the bathroom. But given the price, location and convenience, it was a good choice, and there are tons of things to do in Barcelona with kids within walking distance.