Ozzie cites two big hurdles: Building composite apps and managing trust boundaries between Web apps. "We\u2019ve talked about composite apps as an industry for years, and it\u2019s finally really happening. We\u2019ve been talking about XML and Web services for a long time...and people are finally using those technologies to weave together systems both within the data center and with partners," Ozzie says. "At the scripting level...mash-ups and page-level composition have proven to be quite useful. Even though it\u2019s not deep, it\u2019s really easy, and you can get things together very quickly, so that\u2019s very powerful. And at the end user level, individuals are bringing together a number of different things that are useful to them in terms of small services, whether inside or outside. You can almost think of this as business intelligence for the masses, and we feel that there\u2019s a huge opportunity within Office, at that level, to help people weave together multiple services. "In terms of managing trust boundaries, one of the huge challenges that enterprises are going to have is...managing trust between components of composite applications. In a services world, if you have a service and you want to incorporate a partner\u2019s composite, a component of that service, it\u2019s very easy to just give them a password and a URL and they have access to all your internal data."We believe there should be significant auditing within service components\u2014such that when you do expose a partner to certain enterprise data...you have a complete record of the kinds of things that their app did."