Steven Moffat has said that the Doctor reacted that way to news of another Time Lord's survival in "Utopia" because he was remembering encountering his tenth self from when he was in his fifth incarnation (as seen in "Time Crash") -- and specifically remembering his tenth self telling his fifth self that he had just encountered the Master. When the Time War finished, the Doctor had just believed that time had been re-written again and he would never encounter the Master, nor any other Time Lord, again. But when Martha told him about the fob watch, he immediately remembered his encounter with his tenth self and realized that that meant the Master had survived and was about to re-enter his life.