>>>The data tier should have rules in place to ensure that all of the required
>fields are present, but for the sake of interface speed and conservation of server resources I see no problem with duplicating this logic in the client.
>
>Isn't the whole point of OOPS avoiding the duplication of logic because at some point the rules may get updated in one place and not another?

In the ideal world, we would have a common store for validation logic, and front -end controls would be able to grab and implement this logic from the BO when they instantiate. Reality is, we're not there yet (although work is being done on a universal XML based Business Rules language that should get us a long ways towards that goal). In the meantime, duplication of at least some logic is a fact of life for distributed systems.