The article is a bit vague in chapter 4 about compression and caching. While caching might be good for the client response times, i would personaly stay away from compression. It adds cpu load to the server and even thou it adds only small amount of cpu usage, it could be used to stress the server remotely.

Also, the article is missing very crucial part of tuning web server for fast response times and big amount of concurrent users: Kernel tuning. There's no mention of even simple parameters like how many file descriptors can be open at any time by user. For big sites this is crucial. And it comes really a requirement if there's any php/database code.

It would also be good article idea if to comb thru php options with apache in mind as default rules for php as apache module are very easy to ddos your machine (namely, no limitations on concurrent database connections)