Does Bitcoin-Qt require that I create a bitcoin.conf file in order to solo mine on my Mac? Does Bitcoin-Qt require that I create a bitcoin.conf file in order to solo mine on my Mac?  I created one after reading the wiki and placed it in Lib/AppSupp/Bitcoin but I am not sure I needed to.  Was I correct in creating this file?  If not, what application besides Bitcoin-Qt is it used for?
As the name suggests, bitcoin.conf is a configuration file to set various options of the bitcoin client.  Details of the file and available options can be found here.

The most commonly used option is to set the RPC username and password (see your other question).  If you only want to solo mine using setgenerate true (which, as I mentioned in my other answer is not recommended), the defaults should be fine and you don't need to put anything in bitcoin.conf.