Via Der Spiegel:

All too often, Europe gets lost in diplomatic protocol. The issues up for discussion between US and EU leaders can become secondary. Most seem primarily concerned with who gets to shake Obama’s hand first or who will sit next to him during the meal. Such questions are debated for weeks among protocol-obsessed bureaucrats in Brussels. At the Madrid summit, the unassuming Belgian Herman van Rompuy, who has been president of the European Council since December, was insistent that he be the first to greet Obama. But advisers to Zapatero, the Spanish host, refused. After all, the Spanish prime minister also currently holds the position of “president of the European Council.”
…A compromise was eventually found. Zapatero would get to say the first “hi,” Rompuy would then be able to sit to the right of Obama at dinner. But soon enough, other EU top brass voiced complaints. The seat planned for Rompuy was actually a privilege reserved for European Commission President Manuel José Barroso, who is in third place on the current scale of most important people in Brussels.
And what about Catherine Ashton, the EU’s new “high representative for foreign and security policy”? Her role at the summit hadn’t even been addressed.