Good Service Tier Dev & Design: What are the common bad practises in communications tier development?

Question

I am currently researching the best practises (at a reasonably high level) for application design for highly maintainable systems which result in minimal friction to change. By "Communications Tier" I mean web services, service buses and general network transmission technologies.

From your experiences, what have you found to be the common mistakes & bad practises when it comes to communications tier development and what measures have you taken / put in place / or can recommend to make the communications tier a better place to be from a developer perspective?

An example answer may include: What is the most common causes of a poorly scalable and extendible communications tiers? + What measures can be taken (be it in design or refactoring) to cure this issue?

I am looking for war stories here and some real world advice that I can build into publicly available guidance documents and samples.

Answer 1

The problem is in the question itself - the "communication tier".

Communication should not be a tier by itself, at most you can think of it as a layer. It should not be physically separate.

Hope that helps.