SharePointMagazine has published a series about SharePoint BIs which is worth looking at. Here are the links:
Intro to SharePoint BI (Part 1)
Sell! Sell! Sell! Why Build a Dashboard Anyway? (Part 2 of 6)
KPIs – Who Am I and Where do I Come From? (Part 3 of 6)
Dissecting Dashboards (Part 4 of 6)