Depends on what kind of abstraction layer you're talking about. The traditional BLL/BOL/DAL architecture is probably the worst. It aims for some kind of fantas

Depends on what kind of abstraction layer you're talking about. The traditional BLL/BOL/DAL architecture is probably the worst. It aims for some kind of fantasy "separation of concerns" between the business layer and the data access layer, but many concerns simply can't be classified as exclusively business concerns or exclusively data access concerns. When people attempt to introduce and enforce such a separation, they end up with all sorts of performance problems.