Depends on the objective. What solution is required as the end result.
I have seen many people using SAP trying to implement their BW module only to realise that they spent 100 times more on the implementation cost and got 3/4 crappy cubes that are 100 times less powerful than what Powerplay can give them. The management got fed up of the endless implmentation that went on for 6 months , fired the BW team and brought Powerplay. Some brought Business Objects for report writing.
Some stick to BW because their requirement was basically Data Warehousing and BW is closely integrated with SAP R/3 but not with 3rd party systems. I know Powerplay and BW both so I see the difference. It's good for Data Warehousing but when it comes to BI then it fails. Creating cubes thru SAP BW is a hell of a job, involves 10 components to build the model and manually link them together, even after that, it requires continuous monitoring, tons of configuration if any change is required and they don't even have a front end. They use EXCEL to view the cube, called BEx by them (Business Explorer). They also have a web version but that hardly stands any chance compared to cubes on Upfront. For Ex: if you need to nest one inside another, you need to go back and do some configuration to tell BW what you want, then come back and do the nesting vs. just drag and drop in Upfront.
Don't know about Peoplesoft and Siebel but I haven't seen anything more powerful than Powerplay for BI though the solutions provided by ERP companies for Datawarehousing is usually good because they integrate their datawarehousing solutions with their own ERP closely and that's about it.
My experience has always been that one should hire a couple of programmers to write programs to transfer data from Production DB to DW DB and from that point on, use a good BI tool rather than the DW solution provided by the ERP Companies. It is much faster, less implementation cost and less chances of failure. Better cubes thru Powerplay.
If the objective is only report writing and if they already have a report writer in place then choosing their own solutions might be a better idea and run the report writer against their DW database.
