janharders - 5:00 pm on Aug 11, 2008 (gmt 0)

look at the error-log, around 11.30 on saturday. also, it might help to have some system-monitoring running (like nagios) to see if something else behaved inappropriate (high load etc). usually if apache keeps running (aka "restart" != "start") but won't take connections, you might get something from the errorlog or you really have to search.
do you have scripts on the server? did you write/check them or do other people upload scripts (shared hosting?)? it might (!) be something where simply all the processes apache is allowed to use, are in use because someone messed up a php-script and has some "sleep($tilljudgementday)"-code in it ... call that often enough and every process will be busy. I know, it's not too common, but I had it once on a server where other people created the websites and I was just doing some administrative works ... took me quite some time to figure that one out.
apart from general failures, if it's a script and you have a lot of scripts, it might take some action to investigate ... if an apache-process segfaults, it won't tell you what the last request was (usually something triggering some bug) and can thus be hard to track down.

but then again: if it's not happening again, save your time, might just have been some obscure hickup that just happens every ten years on a saturday at 11.30 ;)