I read the title of the Liquid Post, "Arduino Pin Replicator Double Shield", and all of a sudden the ideas started flowing. I could imagine an Arduino with detachable protoshield on one side and an xbee shield on the other end.
After a week of thought I had to put my ideas on the liquidware site, a 'Double Wide' shield would be much better for my application.
So I uploaded another crappy paint image with a horizontal shield layout.
After a few months and lots of thought the Liqudware community came up with the Double Wide Extender Shield, which is shared with the community at Liquidware.com.
Check it out at Liquidware.org.