Currently in the process of rewriting a few of my tutorials, and have just finished the first of possibly more twitter chapters. We show you how to send tweets that include plain text and also data from an Ethernet-enabled Arduino board without any paid external services.
I understood http://arduino-tweet.appspot.com/ to be an external service, no?
The library uses this site as a proxy server for OAuth stuff. Your tweet may not be applied during maintenance of this site.
I was thinking along the lines of something like Temboo, cosm etc. - things you have to pay for.