I still believe in the application layer concept, particularly on critical systems. I've even added an ETL 'layer' where I have dedicated servers handling inbound and outbound traffic that hit critical databases. I've also found it a good place to deploy legacy vendor solutions that I have to support which are more often than not written *ahem* expeditiously. Some modifications are required and it adds to the overall system complexity a bit but the stability and flexibility are worth it so long as you pay it a little attention.