CIO — Ozzie cites two big hurdles: Building composite apps and managing trust boundaries between Web apps.

"We’ve talked about composite apps as an industry for years, and it’s finally really happening. We’ve 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’s not deep, it’s really easy, and you can get things together very quickly, so that’s 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’s 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’s composite, a component of that service, it’s 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—such 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."