Ajax
There are already several initiatives underway to bring Ajax functionality to Zope/Plone. Here are a few of them:
Azax / plonekukit
Godefroid Chapelle provides a report of the Bern Ajax sprint and discusses several products that were developed during the sprint: azax, kukit and plonekukit.
Godefroid's CompositePack product is already utilizing azax to provide drag-n-drop rearrangement of portlets without a page refresh, similar to Nuxeo's CPSSkins product.
Bling
Ben Saller describes his approach to Ajaxification of Zope using MochiKit, Prototype, Scripaculous and OpenRico. He's wrapped up all of these libraries into a Zope product called Bling.
ZPDojo
Michel Pelletier has packaged up Dojo 0.2 for use in Zope/Plone and has released it as ZPDojo.
jsonserver
Jsonserver for Zope2 dissolves the client-server communication barrier by enabling to directly call any method or template from the client javascript code, with parameters and return value conversion (including composite data structures). Offers Five support and full client compatibility with Zope3.
PloneJSOrder
Andi Zeidler made a simple tool PloneJSFolder to let you reorder items in a Plone folder by clicking on the arrows without having to reload the page each time.