I just installed the plugin wp-cache. I'm not sure why more WordPress users don't enable this. From the Wp-Cache description:
WP-Cache is an extremely efficient WordPress page caching system to make you site much faster and responsive. It works by caching Worpress pages and storing them in a static file for serving future requests directly from the file rather than loading and compiling the whole PHP code and the building the page from the database. WP-Cache allows to serve hundred of times more pages per second, and to reduce the response time from several tenths of seconds to less than a millisecond.
I don't know how many times I've gone to a link on Digg.com and found an unusable site with mysql database connect errors, or simply a crashed web server. The comments always say "Another WordPress Blog".
The problem isn't WordPress specifically. Any site with a database backend for storage could have the same issues. The problem is that WordPress doesn't cache pages by default. Any site serving static content with Apache as a front end should be able to handle digg traffic for a while assuming that they enough memory, bandwidth, and the apache directive "MaxClients" set high enough. Well, WP-Cache turns your dynamic WordPress installation into static pages and only regenerates them when they change.
We were marveling at the efficiency of this all when Scott's Site was dugg twice on the same day.