On the last day of MIX I attended a session about performance and AJAX.  Toward the end of the session Emre Kıcıman talked about a project he is working on in the research labs over at MS, called AJAX View.  Here is what the project site has to say:

The Ajax View approach is to insert a server-side proxy (or web server plugin) in-between the web server machines and the end-user's browser. This proxy captures the web application's JavaScript code as it is being sent to a browser and rewrites the code to insert extra instrumentation code. The injected instrumentation code runs with the rest of the web application inside the end-user's browser and can capture performance, call graph, application state and user interaction information, providing visibility directly into the last hop of the user's experience.

The demo of the tool looked awesome, and at the end of his presentation he asked for feedback.  Look for it to be released soon....