A "neato’ technical article from last fall on using XML and Web Services as data sources in SQL Server Reporting Services. Not sure how I feel about the XML but I had been wondering how to access certain values in SSRS in a web.config type fashion. For generic things like the name of the client logo and the location of said logo.
The idea of using web services as data sources does provide some interesting possibilities where a report with data from the existing system needs to pull data from a third-party where the reported data doesn’t need to be permanently stored just available for the occasional report. Or a situation where the data is "too sensitive" to be stored in the reporting database but can be made available in reports through a web service.