It's getting close to the 2 year anniversary of when I first started using AxKit . Ever since Matt Sargent posted his success story on axkit-users I've been thinking about my own success story with AxKit, it's been highly satisfying.
Matt followed up by saying:
Currently around 10 backend servers (two separate sites) doing about 5 million "hits" a day (almost all of that is the spam incoming from our mail servers, and is handled by a lightweight mod_perl handler, not AxKit). I say "about" because we don't monitor the traffic very carefully - we do problem based reporting - we're not interested in maximising our hits :-)
In my experience with my site having been slashdotted and boingboing'ed (I had in one day 120 000 hits and 19 000 pages without breaking a sweat) the performance has been very smooth on a minimal box. This is all due to caching - when I left caching off another time the server got totally slugged (oops) due to a boingboing'ing.
I never replied to Matt's thread but I want to say that when I picked AxKit it was partially due to the promise of fantastic scalability due to caching - and that's been borne out for me by experience.