I have been using Anthem.Net in few of my projects and have enjoyed the ease of implementing Ajax with it. However, one thing I noticed is that when Anthem does a call back it actually posts the whole page as normal post back, then retrieves the page content in similar way. The underlying javascript then updates only the controls that are marked for update. This definitely is a tricky way of doing a call back which adds little more flexibility, however, the expense of the call back is similar to that of a page post back.I have asked Jason if he's given a thought on doing it little differently. Let's see what he has to say. Any thoughts on this anyone?
Also, I have been exploring Atlas these days. There's a webcast about Atlas in MSDN Events, which shows some quick examples on how to implement it. If you haven't been tuning to the Asp.Net webcasts check out www.learn2asp.net