Saw this mentioned on the Jifty dev list: http://brad.livejournal.com/2329271.html?thread=13756599#t13756599
Previously we did the "preforked pool of servers all doing blocking accept" thing, but that didn't allow scaling of the pool size to deal with demand. So instead, I sat down with some of the Apache httpd guys, went over how Apache 2 preforking and pool scaling works, and came up with a pure-perl implementation. That's what we now use.
Just in case anyone feels like rewriting qpsmtpd-prefork (again)... John
