This is a good idea and I appreciate some of the distinctions in the accepted answer. Since both enumerations and especially interfaces are by their very nature dependency-less this gives them special properties and makes them immune from circular dependencies and even just complex dependency graphs that make a system "brittle". A co-worker of mine once called a similar technique the "memento pattern" and never failed to point out a useful application of it.
Put an interface into a project that already has many dependencies and that interface, at least with respect to the project, comes with all the dependencies of the product. Do this often and you're more likely to face situations with circular dependencies. The temptation is then to compensate with patches that wouldn't otherwise be needed.
It's as if coupling interfaces with projects having many dependencies contaminates them. The design intent of interfaces is to de-couple so in most cases it makes little sense to couple them to classes.
