I've been struggling in searching for proper pointcuts for dojo ajax calls.
The problem is that I'm using JsonRest with DGrid and pagination plugin -- actually it's not a "problem" because I chose to do so in order to shorten the development cycle for core frontend functionality. However, this combination doesn't offer the solution to several minor issues. For example, I want to show a loading picture, instead of just a loading message.
I decided to use aspect advice functions, which is a great piece of functionality available after dojo 1.7. It's not so easy to find the pointcuts to define advices. Reasons are here: http://dojo-toolkit.33424.n3.nabble.com/dojo-aspect-before-function-not-firing-td3985714.html#a3998683 )
In the end, I got some workaround to advise on _create method of dojo/request/xhr. But as I mentioned it's not a nice solution. Hopefully sitepen guru could expose some pointcuts in future releases.