Implementing asynchronous callbacks in asp.Net 4

Internet application development can be seen as the a stateless client-server programming using a thin client.In case that we don't like this approach, we have several methods to change it.
The cause of such adaptations most often stems from specific business needs and rules.

Sometimes, software engineers want to make the client a bit more thick. They usually do this by adding code to the client side, i.e. JavaScript, vb-script, etc. Other times, want to make UI more... feasible. By 'feasible' I mean that it is not necessary to post-back a whole page just for a very simple calculation. One solution to this issue is to put simple calculations to the client side (using JavaScript). But again, what if the operands are members of  some more generic object that cannot be transferred to the client, such as a large database table? Is then the post-back a one-way solution? Well, no. The answer can be called AJAX or in other words (a more MS oriented ones) Asynchronous Callbacks.

Hunting asp.net Authentication and Session Ghosts

Asp.net handles the features of user authentication and user session in two different ways that sometimes may produce ghosts (bugs difficult to find) in our web applications.

The default forms authentication time is 20 mins. Session timeout is extended (to another 20 mins) for every request made to the server.
The default session time is 30 mins. When sliding expiration is true (that is the default), authentication timeout is extended for every request made to the server only after the first half of the total authentication time. The extension time is another 30 mins.