The button rewards do vary but there are a couple of things you can try to ensure that you receive buttons for your reviews.
- Make sure your review is not too short.
- Ensure that your review is original in content, no copying and pasting the same review.
- Do not forget to rate the set you are reviewing.
Read the reviewing guide: http://www.rw-designer.com/feedback
See this blog entry for more information on How to earn BUTTONS.