Moving applications off the profile's main page could have a big effect. Although users can search for interesting applications in Facebook's application catalogue, they can also install them when they notice them on their friends' profiles. "A very large portion--upwards of 20 percent--of application installations now come from the profile," says Nick O'Neill, owner of Capital Interactive, a company that provides social-media consulting and Facebook-application development services. (O'Neill also runs the blog All Facebook.) It remains to be seen, he says, how the changes will affect that number.

The redesign is in line with some of Facebook's recent policy changes. In a June post on its developers' blog, the company writes, "Users must not be surprised by the outcome of an action they take." The redesign includes controls that give users the ability to finely tune what applications can do to their profiles.

"The profile redesign is going to change the application landscape entirely," says Jia Shen, chief technology officer and cofounder of application developer RockYou. "What I always say is that developing on a platform, especially Facebook or a social-networking platform, is like playing a game where the rules change every couple of months. This is a big rules change for the ecosystem."

Shen notes that, in addition to adding the boxes and favorite-applications tabs, Facebook is changing the rules for posting notifications on users' profiles. Facebook will also ask users to opt in each time an application requests access to additional profile information, rather than simply granting the application blanket access during installation. Shen expects the change to make users a bit more squeamish about giving applications access, but he hopes to allay their fears with graphics that help them understand what they're allowing RockYou's applications to do. Shen says that RockYou has plans to promote the use of application tabs in hopes of getting a jump on its competitors. He notes that the first applications users add to the tabbed section will have an advantage, since the new design makes the first three applications the most visible.

Justin Smith, a product manager at application developer Watercooler, who also analyzes the development of Facebook Platform on Inside Facebook, says that the changes could help intrepid developers shake up the status quo. He notes that some developers have found it hard to attract new users since the initial rush. "I think that any time there's a structural change in the ecosystem, there's new opportunity, because not every old developer will be quick to adapt to the changes," Smith says. New applications that make good use of features such as the application tabs might have a chance of upsetting the current leaders, he points out.

But Capital Interactive's O'Neill thinks that developers won't build with Facebook Platform forever. "The real question is, what are people doing when they're on Facebook?" he says. "They're either looking at profiles or managing their contacts. The other things people do are really not limited to Facebook. You can already go play games anywhere else on the Web." He thinks that tools such as Facebook Connect, which allows developers to bring features of Facebook into their external sites, could ultimately become more attractive to third-party developers and reduce use of Platform.