We want to share with you some of our experience using Varnish (https://www.varnish-cache.org) to make our Drupal solutions perform much better.
Varnish is really, really fast. It typically speeds up delivery with a factor of 300 - 1000x, depending on your architecture and this is of a great help for normally not that very fast Drupal solutions.
Knowing varnish can help both a small team company (or a freeelance developer) to optimize their hosting costs and deliver better customer experience and a company that is trying to build a large scale Drupal installation (there using Varnish is a must!).
We (me and a colleague that will be the main presenter: https://drupal.org/user/1845398) will based on our experience share with you some of the configurations we use on our production environments that are optimized with the way Drupal send headers so the caching and utilization is optimal. We will also show you what Drupal modules we use to integrate Drupal with Varnish.
The presentation will be in English as our German is still a bit rusty :) (Hopefully soon I will stop writing that!)