Autogenerate primary key (Guid) Entity Framework CTP5

I have a following POCO class

public class Account
    {
        [Key,DatabaseGenerated(DatabaseGenerationOption.Identity)]
        public string AccountId { set; get; }

        public string FirstName { set; get; }

        public string LastName { set; get; }

        public string Email { set; get; }


    }

I get the following exception when the database gets created

Identity column 'AccountId' must be of data type int, bigint, smallint, tinyint, or decimal or numeric with a scale of 0, and constrained to be nonnullable.

Shouldn't you have:

    [Key,DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid AccountId { set; get; }

?