How can I omit things from the log file?

With log files, would it be possible to add a few more items which can possibly be omitted, such as OOC speech. Or, even better, could it be made fully customizable so anyone could add any number of strings they wanted omitted?

That is easily done now. Set up a trigger to match what you want to omit from the log file, leave the "Send" box blank (so it doesn't send anything back to the world) and check "omit from log file".