Session as a state storage method is rough in high traffic systems for several reasons.
First, the default Session storage method is in-process, meaning that if you have a load-balanced web farm, you'll constantly 'lose' Session information as a user gets pages served from different servers.
The in-proc Session server also dies when an app pool is recycled, which happens more often on higher traffic servers.
The scalability options for Session data are
- Use the freely available ASP.NET
Session Server and point all your
applications at it
- Use SQL Server to store Session data.
Due to the nature of Session data in general, neither of these is a very good option for a very high traffic site (unless you have unlimited money to throw at the hardware).