One of the best examples of this in action is the new beta version of CitySearch, seen here. The site now shows reviews of bars etc from friends, giving the site more credibility (lots of local sites suffer from users posting unreliable reviews, either settling scores or boosting friends). Sadly when I logged in (the process is so easy) I couldn't find any reviews from Facebook friends, but here is an example of how it does work.
Other sites that have signed up include Hulu, Digg, TheInsider (also now live), CBS and Discovery.
Here's an excellent presentation from Razorfish looking at the potential of Facebook Connect (& other similar initiatives like MySpaceID and Google Friend Connect) on sites like Amazon, iTunes and iPhone games.