To be brief, enabling "Remote Access" from the Sharing preference pane enables remote login via ssh as well as the secure ftp (sftp) server. You do not need to enable FTP Access in the Sharing pane to get the secure FTP server.
For some reason, I always thought you needed to enable both to get sftp, but I was wrong. If anyone else is under this confusion, you can disable the FTP server. There is no real excuse for anyone to use regular FTP any more, what with the proliferation of SFTP clients on Mac OS X, Windows and Linux.
[robg adds: Yes, this is a basic tip, but for those new to the various remote access options offered in OS X, they may not be aware of the relationship between ssh and sftp.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060522193940831