Thanks for the tip picobit, but my Library isn't hidden (I unhid it a while ago) and having used the bootstrap.dat method of downloading the blockchain, I had already discovered HardDrive/Users/Username/Library/Application Support/Bitcoin, but there was no bitcoin.conf file there (or in any of the sub-folders).  I created one anyway using Text Edit and included a few versions of the recommended settings (including listen=1).  And I made sure to kill the .txt extension on the filename so that the extension actually was .conf.  None of that worked, it just left me with the following error message when opening Bitcoin Core:

"Cannot parse configuration file: the options configuration file contains an invalid line '{\rtf\ansi\ansicpg1252\cocoartf1343\cocoasubrtf160'.Only use key=value syntax"

...and then quits out of the launch process.

I'm running 10.10.1.

Thanks,
NBTCG