Just as an aside to WordPress optimization, so there are two ways to do that. One of them is to analyze content flow (how often are things updated) and traffic flow and then come up with a reasonable strategy. Things like use memcaching for sidebars, separate those out depending whether you need to, then work on caching plugins. The caching plugins need work because they tend to be programmed to allow robots to spider uncached content, which makes no sense to me. Robot traffic on high volume sites is just insane. With a hundred blogs or so on a multisite installation you could easily spend a month doing postmortems and hunting down the least common denominator (oh hello switch_to_blog, why do you use 36 MB of RAM on each call?)
Or, you can slap some ram sticks in the machine, install varnish-cache, write a few rules for it and go play minecraft the other 29 days.
Or, you can slap some ram sticks in the machine, install varnish-cache, write a few rules for it and go play minecraft the other 29 days.