I took the Compass-Growl gem and modified it to work with the terminal-notifier.
In the Compass config.rb I just added this...
EXCEPTIONS = [StandardError, ScriptError]
begin
require "notifompass"
rescue *EXCEPTIONS
puts "You don't have notifompass gem installed."
begin
require "compass-growl"
rescue *EXCEPTIONS
puts "You don't have compass-growl installed either!"
end
end