My colleague and friend Chris Tavares, who is the Dev Lead on Enterprise Library and Unity, published an insightful article in MSDN magazine on the usage of DI in APIs, which I highly recommend. It is based on our recent experience of doing architectural refactoring of the Enterprise Library. It outlines our design objectives and the approach taken to meet them. It concludes with lessons learnt and key considerations when designing your own API or framework.
Read Chris’s article here.