Brad Peters wrote an interesting article entitled "On-Demand Business Intelligence Takes Off" at  Interesting article and worth a quick read as he explains why an on-demand BI solution makes sense.  Brad states that "It has been said that only 20 to 30 percent of the total cost of a traditional on-premise software platform is license cost – the remainder is the cost of implementing, managing and operating the software (people, hardware and other resources)."  In my experience, I have found that there is a huge customization cost in the BI world and users often just want to pull their data to Excel and work from there.  In fact, in his keynote at SAP Sapphire this year, Hasso Plattner commented that many users pull their data from SAP BW into Access and from there into Excel.  This is an important point to note as Hasso says this is not appropriate.  Even for on-demand BI, it will be important to make sure we have good connectivity to Excel as this is the application that most business users are comfortable in.