There is a distict lack of good material about PerformancePoint Server around, so I was very glad when someone pointed me in the direction of Craig Utley's book.
I have a background in SharePoint and have a good grasp of the concepts of databases and analysis cubes, but I was stuggling to get to grips with the "why and how" for PerformancePoint before picking up this well-written book.
Both the business challenges and how PP adresses these are covered here, before stepping into the how-to sections, where clear examples are used.
A good book for both business Analysts and IT techies in my opinion.
NB: (Product News from Microsoft Feb09) Current news is that PerformancePoint Analytics features will be pulled into the next version of SharePoint Server. The PerformancePoint Planning parts may be sidelined rather than developed further in future.
(Considering the large number of SharePoint servers out there, getting these PP Analytics skills early could be a smart move.)