I've used the services of Pingdom for a long time to keep track of how my websites are loading.

We have mentioned before that both Pressflow 6.x and Drupal 7.x (but not core Drupal 6.x), disable page caching when a session is created for an anonymous user.
An extreme case of this happened recently, because of a perfect storm.

Just going to DrupalCon to watch is awe inspiring.  The amount of people there, all sharing one common goal: to learn more and grow the power of Drupal, thereby empowering themselves...

You can either get on the Drupal 8 bus now, or get run over by it later.