The downside of FTP is it's not disk/GUI based sharing. You can't mount and run apps off of it like AppleShare.
I'm presently connecting to a 10.5-running PPC server from my 10.6-running Intel laptop via FTP. (Go -> Connect to Server -> Typed in "ftp://MacServer.local") It mounted the root of the server as a new network share "/" on my desktop. I can browse it exactly the same as an AFP-connected share. (Although it is much slower.)
And I just launched AppleWorks 6 over the FTP connection. (Yup, AppleWorks 6, a PPC-only app.) When I double-clicked the icon, I got a warning "The application "AppleWorks 6" is on an FTP server. Are you sure you want to open "AppleWorks 6"? Applications may not run or may run very slowly when opened from an FTP server."
Update: AppleWorks refused to load. I did successfully load TextEdit, RealPlayer, and Sound Studio though. (TextEdit the 10.5-shipped Universal binary, RealPlayer 10, a Universal binary, and Sound Studio, a PPC-only app.)