I've seen many implementations of draggable divs in jQuery, .Net Ajax, and plain old javascript. While they are all novel, and solve the problem with varying ease, I've never understood what the point was.
What is the value of a draggable div? What use case does a draggable div implement?
Are there places where draggable divs improve the user experience, or are they the web 2.0 version of the <blink> tag?
No no no...they are NOT in any way like the blink tag.
There are many use cases. Notice iGoogle home page. The user interface is quite easy to use and modify because of draggable divs.
Selecting multiple items from a list is another use case. The blogspot blog page editor uses draggable divs to help you rearrange your page. Like with everything else the features on your user interface must make sense to the user. If something can be moved by the user on the page then a draggable div is a good idea. Without it, a trip back to the server might be necessary.
The use of draggable divs gives the user a sence of interactivity within your website. It gets them involved and allows the to view things on a page the way they wish.
I would imagine that they serve an important purpose in any user interface in which the ability for the end user to visually reorder or sort the entities represented by the divs is important. In addition, I imagine they play an important role in implementing drag-and-drop interfaces in browsers.
Actually I never really found a use for draggable until I realized that you could connect them to Sortables with the connectToSortable param.