I think both those roles are evolving quite quickly at the moment. The classic Enterprise Architect is having to find new ways to plan, communicate and check quality as more and more teams explore Agile methodologies. The Solution Architect is suddenly playing a more obvious role as a result of the above.
My feeling is, it is not so much about people, but about function. The same person could operate as a Solutions Architect most of the day, but then could get together in some kind of Architect's forum and play the role of an Enterprise Architect. That forum then wrestles through the Enterprise Architect issues and establishes the back-bone on which the Agile Development is done.
That's what is probably happening, formally or informally in a lot of dev teams at the moment.