Here is the description directly from Facebook. Some points are really debatable since most people have no clue what is really happening in behind the scenes after we a user click on "accept" when we want a application on facebook.
Facebook Connect is the next iteration of Facebook Platform that allows users to "connect" their Facebook identity, friends and privacy to any site. This will now enable third party websites to implement and offer even more features of Facebook Platform off of Facebook – similar to features available to third party applications today on Facebook.
Here are just a few of the coming features of Facebook Connect:

Trusted Authentication
Users will be able to connect their Facebook account with any partner website using a trusted authentication method. Whether at login, or anywhere else a developer would like to add social context, the user will be able to authenticate and connect their account in a trusted environment. The user will have total control of the permissions granted.

• The main problem here is that the average user does not know exactly what permissions they are allowing, and think that by default facebook is providing adequate protection. They are providing protection but how much?

Real Identity
Facebook users represent themselves with their real names and real identities. With Facebook Connect, users can bring their real identity information with them wherever they go on the Web, including: basic profile information, profile picture, name, friends, photos, events, groups, and more.

This is where it opens up a whole can of worms. More and more people are being victims of identity theft, and when people accept these connects, who really knows what our information is being used for. Do you know what they are doing with your information?

Friends Access
Users count on Facebook to stay connected to their friends and family. With Facebook Connect, users can take their friends with them wherever they go on the Web. Developers will be able to add rich social context to their websites. Developers will even be able to dynamically show which of their Facebook friends already have accounts on their sites.

• I have seen many users with friends in their list they do not even know. Would you want these people having access to your information? For all you know they are in your list to gather as much information on you and your friends; such as email addresses phone numbers etc to then sell it. The question is sell it to who?

Dynamic Privacy
As a user moves around the open Web, their privacy settings will follow, ensuring that users' information and privacy rules are always up-to-date. For example, if a user changes their profile picture, or removes a friend connection, this will be automatically updated in the external website.
These are just a few steps Facebook is taking to make the vision of data portability a reality for users worldwide. We believe the next evolution of data portability is about much more than data. It's about giving users the ability to take their identity and friends with them around the Web, while being able to trust that their information is always up to date and always protected by their privacy settings.

• Again most people have no idea these settings exist nor even understand how to change them.

Facebook connect has been used for some time now, yes there are some interesting connections to be made, but just keep in mind that you are allowing 3rd party access to your information and most times you do not even know what information that is. Get familiar with your "account - privacy settings section as this is where your life on facebook can be seen.
ATP Informatique Team