Microsoft Enterprise Library has survived throughout the years. It has changed a lot, defying a bit the "consistency" principle. If you implement the library and later decide to upgrade to the latest version because a bug was fixed or a feature you need has just been added, it is quite possible that some other software will break. Unit Tests and refactoring are there to help but it is just additional work.
- Library home page - link
- Design Guidelines for Exceptions (link)