Database Schemas are just containers – they aren’t users or anything else – think of a sub-directory on the hard drive. In early versions of SQL Server we “hid” schemas, placing all objects under “dbo”, which gave the erroneous perception that Schemas are users.
In SQL Server 2005, we “un-hid” or re-introduced schemas within the database. Users can have a default schema (a place where their new objects go), you can add new schemas and transfer objects between them, and they have many other benefits.
But I still see a lot of applications, developed by shops I know as well as vendors, that don’t make use of a Schema. Everything is piled under dbo. I completely understand this – since permissions can be granted to a schema, they feel a lot like a user, so it’s just easier not to worry about both users and schemas when you create a database. But if you’ll use them properly you can make your application more understandable and portable.
You should at least take a few minutes and read more about them – you owe it to your users: http://msdn.microsoft.com/en-us/library/ms190387.aspx