I have done some work in this area, but it is not documented well (or even at all really).
I developed a module that includes two key components for performing AJAX stuff:
UITable : A table to list records, but using Ajax to feed the content of the table.
UIForm : A dynamic form to edit a record using AJAX. Actually it uses a combination of iframes and AJAX for this.
The github repo:
A demo action showing how to use it:
And associated template:
And associated Javascript using both UITable and UIForm
There is also a lower level API for just loading and saving records. This is part of the Xataface core:
Steve