As soon as I upgraded to Snow Leopard, my mastery of the hardware serial port looked decidedly unhealthy:
peter@McMullen ~/Documents/saphum $ irb -r ifos/ifos.rb
/Library/Ruby/Gems/1.8/gems/ruby-serialport-0.7.0/lib/serialport.bundle: dlopen(/Library/Ruby/Gems/1.8/gems/ruby-serialport-0.7.0/lib/serialport.bundle, 9): no suitable image found. Did find: (LoadError)
/Library/Ruby/Gems/1.8/gems/ruby-serialport-0.7.0/lib/serialport.bundle: no matching architecture in universal wrapper - /Library/Ruby/Gems/1.8/gems/ruby-serialport-0.7.0/lib/serialport.bundle
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `require'
from /Library/Ruby/Gems/1.8/gems/ruby-serialport-0.7.0/lib/serialport.rb:1
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:36:in `require'
from ../modbus/modbus.rb:25
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `require'
from ./ifos.rb:19
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `require'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/irb/init.rb:253:in `load_modules'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/irb/init.rb:251:in `each'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/irb/init.rb:251:in `load_modules'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/irb/init.rb:21:in `setup'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/irb.rb:54:in `start'
from /usr/bin/irb:13