About new great feature ..

"A field which allow you to set up easily an AJAX Cascading Drop-down list: for example a drop-down of cities (dynamically populated) after the selection of a country." 

This I really looking forward to test bcs this have been something that Joomla should have in core really! 

If you also could have the same for a group selector where  if it could be used so the following scenario can work.
1. User choose usergroup A and then the fields a,b,c,e, f, g only shows up.
2. User choose usergroup B and then the fields a,b,c, f, g, h  only shows up.
So depending on your choice of usergroup you get some reg fields populated for just that user group..
Then you can connect different content, by for example new Joomla tagging system ie example menu of tagging, to different user groups and users by ACL ? 

well something like that...  :)