rails 3 plugins

having a bad time trying to get a plugin to work in rails 3 especially
the Railtie doesn't seem
to be kicked off. Do I need to include Railtie class in plugin or
only in gem? Maybe
someone can enlighten me on the how plugins work in Rails 3

This should be useful for you:
https://gist.github.com/af7e572c2dc973add221