Gojko Adzic – Put the web server on a diet and increase scalability:

"HTTP sessions are often used to store frequently accessed user-specific information, but that is wrong. It is error-prone from the consistency perspective, but it also significantly inhibits scalability.

[…] I strongly suggest using a proper caching mechanism instead of session objects for on-demand caching and optimising access to frequently required information. This caching memory can be released at any time, does not have to persist and does not have to be synchronised across requests."