Some of the references I have been looking at today:
http://www.kenburbary.com/2009/08/five-reasons-companies-should-be-integrating-social-media-with-facebook-connect/
Increased Registration - Data from Facebook states that sites that use Facebook Conect as an alternate to account registration have seen a 30-300% increase in registration on their sites.
• Citysearch.com – Daily site registrations have tripled in the 4 months since Facebook Connect testing began
• Huffingtonpost.com – Since integrating with Facebook Connect, more than 33% of their new commentor registrations come through Facebook
• Cbsinsider.com – Over 85% of all new user registrations are coming from Facebook Connect
http://www.simtechnologies.net/facebook-connect-integration.php
"according to the current statistics using facebook connect increases 30-40% user traffic as compared to non-facebook connect websites."
http://wiki.developers.facebook.com/index.php/Connect/Authentication%5Fand%5FAuthorization
Our research has shown that sites that implement Facebook Connect see user registration rates increase by 30 - 200%.
No Need to Create Separate Accounts
In general, it's not a good practice to force a new user to create a separate account when registering on your site with Facebook Connect. You'll have the user's Facebook account information, and can create a unique identifier on your system for that user.
Just make sure you understand what Facebook user data you can store, or simply cache for 24 hours. See Storable Information for details.
If the user ever deactivates his or her Facebook account, you have a chance to contact the user to request the user create a new account on your site. When a user deactivates his or her account, we ping your account reclamation URL to notify you of the deactivation. Then Facebook sends the user an email regarding the deactivation. If the user has connected accounts with any Facebook Connect sites, and if your site has specified an account reclamation URL, the email will contain a section with your application logo, name, and reclamation link, in addition to an explanation about the link's purpose. For more information, see Reclaiming Accounts.
http://www.chrisbrogan.com/how-facebook-connect-points-the-way-towards-velvet-rope-networks/
The Drawbacks
Though there are advantages to using Facebook Connect for integration, there are some drawbacks, mostly from the marketer’s point of view. If you build out a social network project using Facebook Connect, Facebook gets all the information and you get none. You don’t get a database of users. You don’t get a way to message people participating in your event, except for “in stream,” the way everyone else is using the app. You don’t have any sense of demographics, nor any control abilities to block trolls or other unwanted types.
Crystal Beasley "All of the FB Connect sites we have built so far have incorporated "standard" accounts as well, even with the added complexity of supporting dual login methods."