A code snippet the allows you to run specific Cucumber Feature/Scenarios that have been tagged

cucumber:tags.md

Add the below command into your pre existing cucumber rake task, within the namespace block.

Cucumber::Rake::Task.new(:tags) do |t|
    t.cucumber_opts = "--tags #{ ARGV.last }"
end

All this does is add the --tags option to the executed command line.

usage: rake cucumber:tags @mytag

For more information about tagging your features see this article on the Cucumber wiki.