with intermitant 500's cropping up ... but im getting nothing in the error log whatsoever

Sounds to me like someone's either supressing STDERR, or the error log isn't where you think it is. If someone's supressing STDERR, that's a bad thing, as it could be masking other problems ... but the webserver should have still reported _something_ if it threw a 500

Most likely is that the server is set up using virtual hosts, or something similar, and is writing the logs to some other place -- not all errors from a given server have to go to one file. (or, I've also run into a problem where I was trying to debug on the wrong system because the client machine had an entry in /etc/hosts to force me to use an alternate server)

Find where the error is being sent to, and look at it, and all should be good. Most likely for a 500, something's being sent to STDOUT before the HTTP headers, and once you can figure out what's being sent, you can find why it's being sent.

It's possible that the server might not log an error if the application generated a 500 header -- but why someone would do that, I have no idea.