Brad at Roman Catholic Vocations (and new papa five times over!) posted a link to the following:
Somebody asked me recently how a vocation begins. At first I thought it a strange question - a vocation begins in the mind of God. But it is proper to ask how we perceive that vocation. In my experience, for many people a vocation presents itself initially as a series of little moments of a certain inner restlessness. You want to do something great with your life. You feel that God wants something more of you. You're concerned about the suffering of men and women - spiritual as well as physical. You enjoy the life you are living now, and yet you feel that there is something lacking. These feelings come and go, like waves on an inner ocean. Like distant whispers of a call that will become more clear in time.
Read the rest, very good from Southwark Vocations blog.