You can find it in the Windows Marketplace. <- new link
Or at least it's supposed to be available. I don't think the Windows Marketplace is open anymore. It appears to have closed:
Windows Marketplace has transitioned from an ecommerce site to a reference site. You will find links to sites such as Microsoft Store, Windows Vista® Compatibility Center, and other destinations with cool and compatible software, hardware and devices that support Microsoft® platforms.
I'm waiting to hear back from Wattpad. The press release does say Windows Marketplace, so they're going to have to explain.
Update: Wattpad gave me a link to the new site. Thanks, guys. (It's not actually in the WM, yet, but it is coming.)
From the press release:
Wattpad, the world’s most social eReading community, has released an app for the Windows Phone 7 that is available for free on the Windows Marketplace.
The Wattpad app is already among the top ten free eReading apps in the Apple Store and number one in the same category on BlackBerry’s App World. With today’s Windows Phone 7 reveal, Wattpad’s app is now available on all major phone types as well as 1,000 additional mobile platforms.
During the past year, the Wattpad app has been downloaded for free over 1 million times per month, as readers search out new content and for ways to connect with authors and fellow readers.
Wattpad attributes the success of the app to readers’ desire to have a more enriched reading experience that integrates other popular online social tools. Known as YouTube for eBooks and Facebook/Twitter for writers, Wattpad has experienced explosive growth this summer, with traffic increasing 30% during August.
The Wattpad Windows Phone 7 app is available for download on the Windows Marketplace.