ASP.NET MVC and JSON and when do you use Async

I wanted to post somewhat of a discussion starter around some of the new technologies that ASP.NET has recently released.
ASP.NET MVC This technology has one huge benefit of allowing you to do unit testing on your site.  But there are also a number of other advantages to it, for example, you can have a web page call commands inside a controller.  This allows multiple pages to call the same command which helps keep things clean.  It also does a pretty good job of separating the code from the presentation layer.  But I did find myself doing a lot of coding like I used to with classic ASP or even IDC where we loop through results and have <%= %> snippets all over the aspx page.
JSON/AJAX These technologies have really opened the door to a lot more asynchronous commands on the web.  They allow you to do lots of small submissions and updates without the need to submit and refresh the whole page.
jQuery ...