I finally figured out why I haven't been able to successfully FTP from Safari the last couple of weeks. Apparently, the latest version seems to require that "Passive FTP" be enabled in order to function correctly. I had shut it off because some (IM/Chat) ports on the Linksys at work were disabled, and it made getting an FTP connection kind of a lottery situation sometimes.
In any case, if you're having trouble connecting to any FTP, you might go to the Network Pane of System Preferences, switch to the Proxies tab and make sure that "Use Passive FTP Mode" is checked. This did the trick for me. YMMV, naturally.
[robg adds: Safari seems to work fine for me with Passive mode disabled or enabled, but perhaps this will help someone who's having an issue with Safari FTP...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030421135422327