My Saves are not working. Mongo says I am trying to insert a document with a duplicate key. I think it's because my objects are serializing with key of "_id" instead of "Id". So I map this like this:

BsonClassMap.RegisterClassMap<Foo>(x => {
x.AutoMap();
var memberMap = x.GetMemberMap(c => c.Id)
.SetIdGenerator(CombGuidGenerator.Instance)
.SetRepresentation(BsonType.String);;
x.SetIdMember(memberMap);
x.IdMemberMap.SetElementName("Id");
});

By my documents still serialize with "_id".