Once you have Rails up and going on Mac OS X Server, you can add useful plugins to extend the functionality and perform some useful tasks.
One such solution would be to integrate with Campaign Monitor so you can subscribe new users/members/shoppers to lists within Campaign Monitor for later mail-outs.
Start by adding some extra required gems to your server:
sudo gem install soap4r
Then, install the very useful Campaigning module:
sudo gem install gnumarcelo-campaigning -s http://gems.github.com
Once you have done this, integration is easy. I will be adding to this article with the source of one of my projects shortly!