Ruby script to check challenge compliance with XMAS Challenge 2011: http://coord.info/GC39Q62.

xmas-challenge.rb

# 
# Installation instructions for Nokogiri can be found at
# http://nokogiri.org/tutorials/installing_nokogiri.html
require 'nokogiri'

#
# Usage: ruby xmas-challenge.rb /path/to/MyFinds.gpx
if ARGV.size == 0
  puts "Usage: ruby #{$0} /path/to/MyFinds.gpx"
  exit 1
end

xml = Nokogiri::XML(File.open(ARGV[0]))
ns = {'groundspeak' => "http://www.groundspeak.com/cache/1/0/1"}

# Parses a date-string (on the format YYYY-MM-DD) and returns the
# december date in the range 1-24 as an integer. Returns nil if the
# date is not in the range.
def get_december_day(date)
  if date =~ /\d\d\d\d-12-(.*)/
    d = $1.to_i
    return d if d <= 24
  end
end

# Maps december dates (integers) to a hash with cache-info.
map = {}

# Stores a candidate match in the map.
def register_find(map, date, code, descr, type)
  return unless d = get_december_day(date)
  
  # Prefer "XMAS" caches.
  return if map.has_key?(d) and map[d][:name]["XMAS"] and map[d][:type] == :published

  map[d] = { :name => descr, :type => type, :code => code, :date => date }
end

# Scan gpx file for potential matches.
xml.xpath("//groundspeak:cache", ns).each do |cache|
  wpt = cache.parent
  code = wpt.css("name").text
  descr = wpt.css("desc").text
  register_find(map, wpt.css("time").text, code, descr, :placed)
  
  if descr =~ /XMAS(20..)U[ -]*\b(\d+)\b/
    register_find(map, "#{$1}-12-#{$2}", code, descr, :published)
  end
end

# Print out results
(1..24).each do |day|
  m = map[day]
  if not m
    puts "Empty: #{day}"
  else
    code = m[:code]
    puts "http://coord.info/#{m[:code]} #{m[:type]} on dec #{day}: #{m[:name]} (#{m[:date]}) "
  end
end

The script requires the Nokogiri XML parser, which you can get from here: http://nokogiri.org/.