One of the features Lion has removed from its predecessors is the native FTP server, which we can enable but by default we do not have it at hand at all.
To enable it we have to go to the Terminal - usual thing - and put this command:
sudo -s launchctl load -w /System/Library/LaunchDaemons/ftp.plist
By cons, to disable it we put this:
sudo -s launchctl unload -w /System/Library/LaunchDaemons/ftp.plist
What we're actually doing when we enable it is telling Launchctl to add the FTP daemon to those who boot up the system, no more, no less.
Source | MacOSXHints