just few bugs I've noticed.
When Create New Joomla Users: is set to "NO", after creating user, there is no password field in user details, so cannot be saved:
When redirection URL in login module is set to any other menu destination except "- select item -" it shows stripped URL without parameters (example: &Itemid=58) which causes page without modules, also when SEF urls turned ON it also show old stripped noSEF URLs
I'm not sure about why there are duplicate fields, but will definitely investigate. As for the no password, that may be a JomSocial bug. We'll test on our page, but having no password is a valid way to create a user in Joomla, and if JomSocial isn't handling that properly... it would affect other things that just Joomla.
As an example, Joomla ships with a GMail authentication and OpenID plugin. Both of these authenticate you against remote servers (similar to what JFBConnect is doing), but in no way can you change your password on those servers from within Joomla. We'll test and see if those authentication plugins work properly with JomSocial, if not though, the best we can do is ask the JomSocial team for their feedback.
duplicated fields are shown only when option "Create New Joomla Users": is set to "NO".
as for no password there are no fields when option Create New Joomla Users: is set to "NO" so you're not able to save other options (name, email, Timezone, language) because it ask you to enter password also.
also check redirection URL bug I wrote above.
Two more but have nothing to do with JomSocial:
Opera 9.63 (portable) not showing Connect button, I turned off all popup stoppers:
IE7 (portable) when clicked to Connect button no popup window shows, I've turned of IE7 popup blocker.
I'm not sure if this happens only with portable apps but it sure is a problem