There are many ways to do it, if you don't need security an FTP server on either the phone or your mac is the way to go, just know that the server can't use the port that FTP normally uses for security reasons (unless you rooted it). Just search for ftp server in the android market and I'm sure you will find something. I personally use an SSH server on my Nexus One to transfer file to and from my phone securely. It's a little more difficult because Finder doesn't support sftp and I have to use the terminal and scp commands. That might not be the way to go though because the server costs money and it's not the easiest way to do it.