A colleague of mine told me of a course he was on recently where a few delegates were tweeting as they took the course - they were at PCs so could do so easily.
Some of the comments weren't all that positive BUT they were picked up by another colleague who had a hand in designing the course. He then fed back some of the Twitter comments back to the trainer.
The feedback was instantaneous and was acted on, so a positive outcome and a demonstration of how Twitter enabled the real-time development of some training.
I think it is important to note that this was a software training course so a) there was easy access to Twitter and b) there were not issues around deleagte confidentiality.
That said, Twitter enables feedback, sharing of ideas and transparency around training which is very powerful in evolving train ing content.