Should and can you use the UserId in the Membership store as a key to tables in the application database?

Hello,

I'm new to RDBMS (SQL Server 2005 Express Edition) and ASP.NET.  Is the best way to link records in an application database to a user in the Membership store  through the UserId?  If this is the best way, can it be done?  I'd like to use the UserId as it is unique and will not change like a User's name could.

I also tried to bind and list users in my Membership store.  I was able to bind and view all the fields of the users in the store except for the UserId.  I got an execution error saying that the "Field or property with the name "UserId" was not found on the selected data source."  Are you able to DataBind the UserId?

Within the Page_Load:

I assigned GetAllUsers to a MembershipUserCollection

then assigned the MembershipUserCollection to the GridView.DataSource,

and lastly did a GridView.DataBind()

I would appreciate any help that you may hav ...