VentureBeat has an interesting story explaining that some companies are seeing a spike in traffic to their sites due to their integration of their applications with the Facebook platform. For example, HotOrNot.com offers a Facebook interface for their site:

Surprise: Facebook apps may help grow home sites

The finding, reported by Quantcast, a service that tracks traffic trends for Web sites, suggests that sites failing to embrace Facebook may be missing out on potential growth.

For some, this is also encouraging evidence that Facebook’s platform, launched in May, isn’t necessarily weening users entirely off their own Web sites. While Facebook allows third-party sites to advertise on their applications on Facebook, many sites prefer to maintain control over their users’ experience, and are hesitant to trust Facebook’s promise that it will remain hands-off. Despite the pledge by Facebook’s executives that sites are free to make money on their apps within Facebook, its terms of service says Facebook can change its policy at any time.

To me, it seems like companies who can enable Facebook interfaces for their applications aren't hurting themselves. They're simply providing access to a larger audience who happens to prefer accessing applications through Facebook rather than on the open web.

In the ideal situation, data gathered through any interface such as Facebook will be treated the same by the application host, and improve the value of the application overall regardless of the interface used to get the data into the system.

This may not apply to all applications, but it seems like it should hold true for web applications that become more valuable as more people participate and contribute information such as HotOrNot, other dating sites, auction sites, wikis, etc.

I think we'll see more businesses trying to decide whether they've better off launching as a Facebook application first, on on the web first with a quick follow-on Facebook interface.