If you (or anyone) is still interested, a quite minimal rakefile could be:
require 'time'
desc 'create a new draft post'
task :post do
title = ENV['TITLE']
slug = "#{Date.today}-#{title.downcase.gsub(/[^\w]+/, '-')}"
file = File.join(
File.dirname(__FILE__),
'_posts',
slug + '.markdown'
)
File.open(file, "w") do |f|
f << <<-EOS.gsub(/^ /, '')
---
layout: post
title: #{title}
published: false
categories:
---
EOS
end
system ("#{ENV['EDITOR']} #{file}")
end
Taken from here.