I'm not sure how it's done on a Mac, but here's how it works on a Windows machine.
Typically it's all stored under C:\Users\<username>\AppData\Roaming\Bitcoin
However, my C: is a small SSD and the databases from BTC and LTC were filling it up fast! So I learned there is a command line paramter (-datadir=) which allows you to redirect the folder to a new location...so I created a short cut like this:
bitcoin-qt.exe -datadir=F:\BitcoinData
The -datadir= optoin on the executable allows it to store the block chain data there. I'm guessing the same command line argument exists for Mac as it does for Linux/Windows clients.
The above still leaves my wallet.dat on my C: drive but the blockchain database stuff is all on my F: drive instead.
Hope this helps.
yeah, in /users/xxx/AppData/Roaming/Bitcoin
in the bitcoin.conf file
datadir=X:\Blah
the only file in my appdata/roaming/bitcoin is my bitcoin.conf file
the wallet.dat and everything else goes into whatever the datadir is
bitcoin-qt might be different, I only use bitcoind