There is one thing which sooner or later appears in our project..., we need to Drag&Drop elements. Well among the good thing about javscript frameworks, we have the drag&drop utilities!!, ..mostly all cover this feature, from Jquery to Script.aculo.us, some of them in a most powerfull which may the one belonging to Dojo (that is one reasons IBM uses it for dragging and dropping portlet on pages).
Here I add links to an example on each (2 of them in spanish).
DOJO: Article 1.
JQuery: Article at Hermoso Día, Article from PaperMashup.
Script.acolo.us: Article at Vagabundia 1, Article at Vagabundia 2
....And check the official websites of this frameworks which also offer help and info on the drag&drop topic!!.