Message recipient selector redesign

When user first goes to Compose a message, the default content for the non-editable To field is "All Site Recipients".  If the user wants to select specific recipients, she clicks the "Select Recipients" link: 

 
A lightbox appears that allows users to select  individuals, groups/sections, or those in a particular role. If user is selecting individuals,  filters help narrow down the list that he/she selects from:
 

If the user wants to add entire groups/sections or all members in a particular role, they can switch to one of the other tabs. Here, she has switched to Groups/Sections. Note that the collection bucket (right hand list) allows for items from each of the tabs (e.g. "I need to send this message to all my gsi's, plus one particular section, and one particular individual".)
 

After clicking the Add Recipients button to close the lightbox, all recipients are listed, comma-separated, in the non-editable field. User can click the first link ("Edit above list of recipients") to display the lightbox again (with previously selected recipients in the right-hand collection list), or the second link ("Set recipients to All Site Participants") if she decides she does, after all, simply want to send the message to all of the site recipients (confirmation box should appear:  "Are you sure you want to send this message to all site participants? This will remove all the specific recipients you previously selected.")