Our system could accept transactions over the phone (via a clerk) or through our website. The clerk on the phone used a semi-web based application to interact with the system.
The headache with this was that the code base for the "semi-web" and "actual web" only became a common code path much, much deeper in the code. So the plan was simple, redo the website code such that it could eventually be leveraged to replace the semi-web code.
We prototyped, mocked up, tested and developed a new part of the application on our website using GWT. It went through load testing, SEO-approval and I believe we even did a couple in-company demos of the technology.
The code was "done" (in the "given to QA to break" sense of the word) when I left, but when I check the website now I see it never made it to production.
I cared about this for the first month or so after I left, so I pinged around to find out what happened. The short version is that it got stuck in developer mythology, and with nobody there to lead it out, I knew it would never see the light of day.
I wonder just how much technology is "done" that has never seen the real world?