If you use Git for Rails development you know that now that migration numbers are UTC timestamps, doing branchy development became a lot easier. When merging, you just have to go back and find out which migrations are new, and run them manually.
Or, with this patch (http://dev.rubyonrails.org/ticket/11493), you run rake db:migrate, and Rails migrates (only) the new ones for you. Please review the patch and +1 if you'd like to see it in Rails.
