It seems that the need to turn on "Socket.do_not_reverse_lookup = true" 
in order to use WEBrick with OS X 10.3 isn't the only socket issue. 
What follows is a basic example of attempting to do a directory listing 
on a public FTP. Note that the FTP connection itself was successfully 
estabilished. It's only when I attempt to ls it throws the following...

irb(main):001:0> require 'net/ftp'
irb(main):002:0> sunsite = Net::FTP.open("sunsite.auc.dk")
irb(main):003:0> sunsite.login
irb(main):004:0> sunsite.ls
SocketError: getnameinfo: nodename nor servname provided, or not known
         from /usr/local/lib/ruby/1.8/net/ftp.rb:295:in `addr'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:295:in `makeport'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:329:in `transfercmd'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:421:in `retrlines'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:419:in `synchronize'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:434:in `retrlines'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:628:in `ls'
         from (irb):4

...attempting the "Socket.do_not_reverse_lookup = true"-trick gives a 
different exception:

irb(main):001:0> require 'net/ftp'
irb(main):002:0> require 'socket'
irb(main):003:0> Socket.do_not_reverse_lookup = true
irb(main):004:0> sunsite = Net::FTP.open("sunsite.auc.dk")
irb(main):005:0> sunsite.login
irb(main):006:0> sunsite.ls
Errno::EPROTONOSUPPORT: Protocol not supported - socket(2)
         from /usr/local/lib/ruby/1.8/net/ftp.rb:295:in `initialize'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:295:in `open'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:295:in `makeport'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:329:in `transfercmd'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:421:in `retrlines'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:419:in `synchronize'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:434:in `retrlines'
         from /usr/local/lib/ruby/1.8/net/ftp.rb:628:in `ls'

Any known work-arounds for this? Is the socket issues being worked on 
in general?
--
David Heinemeier Hansson,
http://www.basecamphq.com/   -- Web-based Project Management
http://www.loudthinking.com/ -- Broadcasting Brain