WordSift is a very interesting application for teaching vocabulary and / or working on texts. It's extremely easy to use and the art lies, I think, in coming up with interesting and creative ways of using it in the classroom. Here's a link to two demonstrations from teachers of how they use this tool with their learners:

To give you some idea of the business English potential of the tool, here is a shot of the word list created when I pasted in the text for You Have to Start Meeting Like This! article on meetings in the Fast Company magazine:

And here is the visual Thesauraus that was also automatically generated:

It would be extremely interesting to hear your thoughts on this tool and if you have any further ideas on how this could be exploited to make textual work more motivating and effective please feel free to leave your comments.