This post is more of a bookmark for me so that I stop bugging the brown stuff out of the John the Siebel-BIP product manager. I have had multiple customers over the past two weeks asking for help around the integration. What's its capable of? How can I allow my users to click a button to run a BIP report? How can I kick off a report from a Siebel workflow?

Start right here - this is a great white paper explaining whats now available with the integration using, the Siebel Report Business Service. Once you have consumed that from start to finish.
Get on over to Oracle support and look for the following note that has code samples and lots of other good stuff!

Siebel BI Publisher Reports Business Service (8.1.1.7+) [ID 1425724.1]

The Reports Business Service enables BI Publisher reports to be executed from the Siebel application via a Workflow Process, or through scripting. The report is generated in the background by connecting to the BI Publisher server. The report output is stored in the Siebel File System and accessed from the My BI Publisher Reports view. Alternatively using appropriate methods, the report can be attached to an entity or sent to a particular delivery channel.