CB Connect has been completely re-designed. All the social sites JavaScript libraries have been removed (except for Fields usage) and replaced with an internal popup jQuery script providing uniformed popup usages across all browsers (tested FF, Chrome, and IE).

All oAuth exchanges are now done server side instead of client side. What all this means is you won't have to deal with conflicts anymore as there is nothing to conflict (JavaScript wise at least). This also means oAuth1.0 and oAuth2.0 are both integrated into CB Connect opening it up for significantly more social sites to be integrated.

You will notice significantly improved page load times with 4.0.0 as well as the 3rd party libraries loading in was the cause of the slow down.

With all that said there are some backwards compatible changes that must be noted. Please review the below carefully.

Google
Redirect URI must be reconfigured to be exactly as specified within CB Connect configuration. Google will stop working until this is done!

Windows Live
Language selection is now gone. Should use the language you specify in your Application.

Facebook
Language selection is now gone. Should use the language you specify in your Application.

Twitter
Tweek Box is now gone (@Anywhere API depreciated).
Profile and Follow buttons are gone (no way to obtain screen_name through API calls publicly)

All
Snoopy is removed. Due to the detailed CURL usages it isn't functional for these usages anymore. You absolutely have to have CURL and JSON available. These are pretty standard so should not be an issue for the majority.

Twitter is of course back and fully functional again in this release.

In addition to all of the above the "Incomplete Registration" page has been completely rewritten. It is now presented to the user before they register. So no more invalid users being stored in your database. If the email address supplied by the social site is already registered the user will see the incomplete registration page asking them to supply a new valid email address (informing them it's in use already as well) or to login to link to an existing account (if linking is enabled).

It's no different then the past releases. So if it never worked properly with your setup then that's still the case. It'll work fine with CBSubs depending on your setup. You can also give social site users a usergroup on registration as needed (defaults to default CB).

No you can't present a registration form for them to complete or anything of the sort as that is against the social sites policy (you can't pre-populate a registration form). It does show terms and conditions, but only if using CBs built in; it will not work if using a custom field for this.