I'm giving a presentation at Bishop's University in Sherbrooke on Friday at noon if anybody is interested. It's called "Managing Millions: Tips and techniques for building high traffic web applications." It will talk about some of the problems that we faced back when I was working on a high traffic website like various database bottlenecks, issues faced when using cache, etc. plus the solutions we used on how to fix them.
Some of it will cover some techniques that we researched but didn't really employ, so I won't be going into as much detail on those. For example, doing asynchronous processing (aka offline processing) which in hindsight I don't think we didn't do as much as we should have and the stuff we did do wasn't very elegantly handled - cron jobs are decent but when you aren't sure how long the script will take you have to do some hacks to make sure that you don't have too many running at once, etc. There's better tools out there for this.