I'm always a little frustrated when people recommend nginx over Apache. No argument; they're both great, but why would you suggest that someone adopt a new technology and deal with those hurdles, instead of making suggestions to their current environment and then guiding them towards future adoption?

Thank you sir for standing up for Apache!

True, and true. The main issue with caching WordPress is that WordPress itself is very dynamic and full of cookies, WordPress has plenty of caching plugins available but as I point out, that wont help you against Apache spawning tens of processes and eating all your RAM.

So therefore you're down to external caching, which is another layer of complexity and detrimental to anything dynamic you have on your blog (which is pretty common).

You're right, it caching won't help directly. But if every hit takes a tiny fraction of a second because it's (at least mostly) cached, it will take a lot more to overwhelm Apache. Caching Wordpress is not trivial, but it's not necessarily all that difficult -- it depends on the particular blog and how dynamic it has to be. I've had success setting up caching for my own stuff as well as a high-traffic online magazine.

Your larger point, BTW, that Apache can be overwhelmed, and that it makes a lot of sense to do some math and tune the configuration -- makes a lot of sense. I'd not really thought about that in depth before, but it seems obvious now. :-)