In this recent post to the In2it blog Michelangelo van Dam makes a recommendation to decouple your logic from your framework to make it easier in the future if you need to replace it.

Decouple your framework or library from your business logic for future upgrades or replacements through usage of interfaces. By separating your business logic completely from the tool used to glue all things together, you can replace your framework or upgrade to a newer version without much problems.

He talks about how it's common for applications to quickly become "good application turns into a cluster of code on top of a cluster of code". While the title suggests completely swapping out the underlying framework, he shifts it to talk more about updates to the current framework, especially ones that would break non-decoupled functionality. He then covers the ideals of "interoperability" between PHP packages based on common interfaces (like the PSRs) and how following a similar idea can help decouple your code to prevent hard work for future potentially breaking changes.