Cypher looks a lot like a form of SQL? At least if you are refering to this one http://neo4j.com/developer/cypher-query-language/ It seems an entirely different beast. Not like something you'd want clients to have access to in a public api?
True but doesn't facebook use it with a graph db? The convention is to replace REST with something that maps naturally to data stored in graph... sort of a structural match query that expects certain kinds of nodes/relationships (unless you manually map it to a relational or document db).