hey for the most part, most roots are blank, but some like lunypages and i'm not sure whom else use public_html, I use /www/htdocs but maybe reading the help file will spread some light on the subject.
http://kellyinfo.com/web/help.jpg
version 6.0 build 3 help file

For what it's worth, here are the settings I use for FTP from within VSD. Host is totalchoicehosting.com.

Hum!
I use a forward slash so I can bypass the files manger in Lunarpages and go right to public_html folder.
Godaddy is blank..
Yahoo is blank
Bravenet is /yourdomain.com
interesting indeed!

I was having the same problem with the latest VSD version and what worked for me was LEAVE OUT the / (slash) after the .com like in the following;

For the FTP Server: mywebsite.com
WORKS!

BUT.. If I put the / (slash) like this; mywebsite.com/
IT DOESN'T WORK!!

I can't believe it was that simple but my problem seems to be solved now.

TW

Yeah I only use / if I have a sub folder basically. but / in front of public_html for me is bypassing the file manger otherwise I'll have to locate the public_htm folder and click on that and then upload, so for me it shortens a step or two.