was sitting here and thinking about for example session id etc, such data could perhaps be stored in a memory table (http://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine.html), I was mostly thinking of specified data that might be accessed often in a short period of time. A possible speedup factor perhaps?
Memory table has certain limits. For example you cannot use text or blog field type, which session table needs.