My opinion so far - Google forms allow you to easily create and embed forms (i.e. blank text fields, multiple choice questions, checkboxes, etc.) and collect the answers, but doesn't provide any way of selecting 'correct answers' or calculating results. Might be useful in some situations, not so much in others.

Help info here:
http://documents.google.com/support/bin/answer.py?hl=en&answer=87809

Screencast on how to create 'Gquizzes' at:
http://www.screencast-o-matic.com/watch/cjXeqwnDe