My experience is that ReportBuilder is already too complex for the majority of end-users. You really need people who can understand data, relationships and can write a (basic) query (SQL, not MDX because this is certainly not for end-users). An analyst with some technical knowledge (often also the company's excel guru) could work with the tool but usually there are not many around. I think they are also the only people who can qualify for any 'self service bi' tool to be honest.