I have created a userData small client-side app that uses the pop up box version 4.0 over at dynamicdrive.com.
For those that don't know the userData behaviour in MSIE allows you to create client-side XML Stores that are larger than cookies.
I comibend multipel pop up windows that have minmize, maximize, drag, and resize with the userData Behaviour methods of load existing, save as current, remove as current, with editable glyphs content areas.
Basically each pop up window can be its own WYSIWYG window with its own persistence and data store all local of course.
A simple use of this would be a networked tag board to leave a current task or top priority message(s). You can have multiple data stores but each data store only retains memory for the last saved item.
userData stores can be used to set prefences as persistent qialities to the end user. They can be used to store posted submitted userData from forms or the editable glyphs regions i mentioned above.
So what is the advantage, for me it allows for a simple local dynamic data store quality to html pages.