Centralized Business Intelligence
My approach as a BI professional has always been to organize the data into conformed structures, present that to end users for consumption in their ad-hoc analysis, and only build formal reports and dashboards as necessary. I think the conformed structures provide great consistency for BI across the enterprise no matter who is building it and allow users to get answers to questions faster.
Of course, there is no way IT can keep up with the onslaught of report requests so it makes sense to provide users with the tools to do these themselves. Typically, I would offer up a connection to a cube through Excel and now with the addition of PowerPivot I believe this type of process is going to become even more prevalent.
Some I have talked with have expressed concern of decentralization of BI by tools like PowerPivot however; I see these tools as giving users a sort of proving ground for their BI applications. If an information worker successfully creates a BI application in PowerPivot that becomes widely used across the enterprise IT does not have to guess that formalizing it into a more formal BI application will have value.
Other methods exist that I think are worth for determining the value of a BI application (eg. BI Pathway Method) however I believe this is for more formal BI versus the ad-hoc type of analysis that users clamor for on a day-to-day basis.