Conclusion

Systems must be clean too. An invasive architecture overwhelms the domain logic and impacts agility. When the domain logic is obscured, quality suffers because bugs find it easier to hide and stories become harder to implement. If agility is compromised, productivity suffers and the benefits of TDD are lost.

At all levels of abstraction, the intent should be clear. This will only happen if you write POJOs and you use aspect-like mechanisms to incorporate other implementation concerns noninvasively.