An absolute requirement is a complete understanding of the behaviour of the underlying components. Especially while integrating packaged applications, this really requires specialist knowledge of the internals of the package. Also, since you have no control of the package, it introduces the risk that changes occur in some of the packaged components, without you noticing. No longer the complex exercises of translating business requirements into functional specifications, prototyping, RAD, etc. Again, this underscores our requirement that EAI must be a business driven exercise.
Business people have to be involved from the beginning.
This also implies that top-management must drive the exercise. EAI is difficult, complex, and expensive. Therefore, you only want to start such an exercise if the potential gains are in balance with the guaranteed pains. However, in today's business climate only very few companies will have the luxury of stability. Again, be realistic and know your business objectives.