The last number I heard from Mike and the PM team was that BIP is now embedded in more than 40 oracle products. That's a lot of products to keep track of and to help out with new releases, etc.
Its interesting to see how internal Oracle product groups have integrated BIP into their products. Just as you might integrate BIP they have had to make a choice about how to integrate.

1. Library level - BIP is a pure java app and at the bottom of the architecture are a group of java libraries that expose APIs that you can use. they fall into three main areas, data extraction, template processing and formatting and delivery. There are post processing capabilities but those APIs are embedded withing the template processing libraries.

Taking this integration route you are going to need to manage templates, data extraction and processing. You'll have your own UI to allow users to control all of this for themselves. Ultimate control but some effort to build and maintain. I have been trawling some of the products during a coffee break. I found a great post on the reporting capabilities provided by BIP in the records management product within WebCenter Content 11g. This integration falls into the first category, content manager looks after the report artifacts itself and provides you the UI to manage and run the reports.

2. Web Service level - further up in the stack is the web service layer. This is sitting on the BI Publisher server as a set of services, runReport and scheduleReport are the main protagonists. However, you can also manage the reports and users (locally managed) on the server and the catalog itself via the services layer.

Taking this route, you still need to provide the user interface to choose reports and run them but the creation and management of the reports is all handled by the Publisher server. I have worked with a few customer on this approach. The web services provide the ability to retrieve a list of reports the user can access; then the parameters and LOVs for the selected report and finally a service to submit the report on the server.

3. Embedded BIP server UI- the final level is not so well supported yet. You can currently embed a report and its various levels of surrounding  'chrome' inside another html based application using a URL. Check the docs here. The look and feel can be customized but again, not easy, nor documented. I have messed with running the server pages inside an IFRAME, not bad, but not great.

Taking this path should present the least amount of effort on your part to get BIP integrated but there are a few gotchas you need to get around.

So a reasonable amount of choices with varying amounts of effort involved. There is another option coming soon for all you ADF developers out there, the ability to drop a BIP report into your application pages. But that's for another post.