I had an issue which I posted here:
http://dojotoolkit.org/forum/dojo-core-dojo-0-9/dojo-core-support/callin...

I propose to have the dojo.xhr* family automatically include the 'this' object as a parameter in the new 'this' that is created in the handler functions.

It could be either passed in as a parameter in the function, e.g.

function_handler : function(response, ioArgs, original_this) { ... }