It\'s not explicitly written somewhere but I felt so after reading few blogs on ASP.NET MVC. Just got curious and thought of asking it here.
UPDATE:
It really depends on how much data you are maintaining in the session state. As a rule of thumb, I try to just use it for a few strings here and there and not much more. For a large form, for example, I might store a reference ID to that session, then store all the needed data in SQL temp tables based on that ID. It is kind of a pain, but the session state is not meant to be used to store loads of information.