Colin, you have to take into consideration that Barca haven't got a manager at the moment. Some people may find it easy to say that they are quality players and do not need a manager to inspire them to victories after victories. Tito Vilanova's cancer relapse, since Christmas has most definitely affected the team. At the start to the middle of the season, they were breaking all sorts of records hence the reason why they are 12 points clear. Vilanova's influence is sorely missed. He is their leader and is highly respected by his team so IMO I wouldn't read too much in Barca's recently poor form.
I think this is a very salient point, and one missed by the majority of people on this post. I'm not a big follower of football in Spain, and only look at highlights now and then, but when was the last time anyone saw a Barca player sent off because he's talking back to the ref about a non-call? They have, for years been a very disciplined team, working as one, implementing the system to near perfection. But to me it’s that discipline which has broken down, and it makes me really wonder is it because there is just not the leadership at the moment.