A few days ago, I heard someone complaining about the risk of introducing a light-weight CMS as an alternative for the default SharePoint (MOSS2007) solutions. The main issue was the amount of learning that would be required to get productive in the alternative environment.
Now let me throw in a bold statement: if your developers have managed to handle the complexity of a SharePoint solution, they can easily learn an alternative. The only risk is that they don’t want to go back ;).