I've used Wordle and other word clouds in various ways in class. A successful example was when the students completed a note sheet online about the three Seminole Wars and then had to create a word cloud about each war to summarize what they had learned. They had to have 10-15 words and/or phrases that summarized what stood out to them about the war. They came out really well and made for a quick, creative check for understanding.
Here's one I created about the Civil War, our upcoming unit;