Considering the form of some of their players at the moment, I could see them going out early even perhaps.
Most of the Spanish players have had very long seasons (likely winning even more silverware, I see them tired and now to add to this out of form.)
Villa, Torres, Silva, Puyol, Piqué, and perhaps even Xavi in some sense are all either out of form or on old, exhausted legs at this point. Fabregas has been sitting on the bench and playing on the perferial of this Barca team. Pedro has been shown to be just another pretty good player, nothing more.
Question is how well they can keep to their style which is so difficult for teams to play against.
Overall though I don't even expect them to make the final. I can see them going out against any of the Portugese, Germans, or Dutch in the semis, and perhaps even France or England (:undecide
could pull off a tight (maybe penalties) win against them as well.
my bet still goes to someone out of group B. Most likely the Dutch or Germans.
Would be pretty incredible if they do manage to retain the trophy though. Would really be known as the decade of Spanish and Barcelona domination.