In the particular project I'm working on we are already using Enterprise Library. I'm researching using it (i.e. Unity) for dependency injection.
The recommended way to include Unity is modify global.asax so that it exists for the entire length of the web application. I'm very reluctant to pursue this route primarily because of the increased deployment risk across multiple servers. A way that can take advantage of SharePoint's solution/feature deployment mechanism is much preferred. Also, Spence Harbar strongly recommends not to modify global.asax.
I noticed that SharePoint Guidance avoids EntLib and uses a Service Locator pattern. For reference, this article shows both EntLib and Service Locator options.
How should dependency injection and inversion of control be implemented within SharePoint?