What do you consider before refactoring code?

Question

I've got an application that just shipped. Since I wrote it, I've learned about amfphp and propel. Both would be 'nice' to be used in the application but I can't say that it would be required at this point.

What types of things do you consider before you refactor code?

Answer 1

Have unit tests to check the code after refactoring.

Answer 2

Effort required versus benefit received and where it fits prioritywise with other work.