In integrating Facebook Connect, Citysearch is perhaps the most interesting example so far of what’s possible with data portability. The beta site allows you to login using your Facebook credentials to write reviews, and also track what other Facebook friends are doing on the site.
In other words, without registering for a Citysearch account, you’ll both be able to leave reviews of different places on Citysearch, as well as see what your friends are recommending. Those reviews are also broadcast back into Facebook, in turn allowing you to read your friend’s Citysearch reviews from your Facebook News Feed. Meanwhile, Citysearch is also expanding their mobile offering, allowing users to submit mobile reviews based on the new hyperlocal listings.