We have apache log level on debug as we are hunting a bug on our magento site (http://stackoverflow.com/questions/11841465/magento-payment-portal-forwards-how-to-debug/11841891#comment15757876_11841891) - we see a lot of these lines in error_log:
The timeout specified has expired: SSL input filter read failed.
Connection closed to child 20 with standard shutdown
(here some complete log line: https://gist.github.com/3289621)
we see, that these lines are logged on info level, but want to be sure, that this is not a problem but a normal condition. (we stumble over this bug report: https://issues.apache.org/bugzilla/show_bug.cgi?id=52703)
we see a lot more of these lines as there are obvious problems (we have problems with forwards to external sites (paypal..) when in SSL mode (at checkout) but want to elminate this.