Ever get sudden spikes in Apache processes stuck sending reply state?
This explains how to figure it out better than I could:
http://techmythsworld.blogspot.com/2011/11/solving-httpd-maxclients-and-modstatus.html
As always, in case this goes away...
Here is a super boiled down bit:
1. Check error logs for Apache 2. Check server status (think mod_status module) 3. See lots of "W"? A. Check for get's with high SS - and growing.... B. Find script where there might be issues with things that are not supposed to happen :-) - this only applies if it happens during random times (i.e. think low load times).