WhitePaper: PerformancePoint in an extranet environment
Great read for when you are stuck in the airport: Publishing PerformancePoint Server in Extranet Scenarios.
This is actually a very detailed document outlining many of the aspects around establishing an extranet deployment, particularly a secure one.
Important Note: We have run across a bug in Server 2008’s implementation of Kerberos. This issue will cause a fatal flaw to your implementation with SSAS in the scenario– Dan English provides a greater level of detail in his post earlier this year. Just as a recap, you will run into errors in accessing SSAS where the MDX will get truncated in the Kerberos ticket that gets passed to the SSAS service. The only way around this at the moment is to have the front end servers be Server 2003, or CTP versions of Server 2008 R2.
Note that there is no "official" fix for this at the moment, though one is expected as a cumulative update in August.