The next days I will have a deeper look into web sites that are using AJAX frameworks that will replace the typical postback used in ASP.NET.
Today I found a new job portal (http://www.dot-net-jobs.de/ ) using the Atlas framework  to allow paging throug a list of job offers. I started Fiddler  to see how the page is using the framework and what data will be transferred during the AJAX calls.
I deleted my local cache of Internet Explorer and entered the URL. After everything was loaded I checked Fiddler to see each request. The default.aspx showing the inital page is about 17 KB, then the Atlas framework is loaded using the WebResource.axd, the size is about 243 KB. Because I'd like to compare this web site using AJAX or not I don't want to have a look at the size of the css file and images (these are cached after the first call).
Now, I'd like to go to the next page using the weiter link (German translation for next). In Fiddler I see the request using the Atlas framework. The request is returning 14 KB html source code, only 3 KB less then the complete initial page showing the same info. Saving 3 KB per page means: we need about 81 clicks on weiter to save traffic!!
One thing you have to look at when using AJAX-styled web applications is that you may lose several features (is not an Atlas only problem, most AJAX framworks do not have an build-in support for these problems):
I hope we will find more and more things where we have to be careful using AJAX frameworks.