Excellent for teachers who don't use a textbook!
I love it and have been using it for years. I just recently upgraded to the teacher version ($25/yr), but I think that needs some more work before it's really great. It's very low-level looking at Bloom's Taxonomy, but vocabulary is necessary to move up!!
How I Use It
I teach German, and do not use a textbook. Instead I create vocabulary lists on Quizlet. Students know to check here if they have been absent to catch up on notes, and we spend about 10 min./week practicing vocab terms in class.
In the past, I've also had students create sets on a topic of their choice. For instance, one student researched Basketball in Germany and came up with a set of vocab, including dribble, shoot, pass, etc. I printed the "Test" at the end of the unit to serve as the vocab synthesis for that element of the unit (there was more to it, of course!)