How do I get the fivestar module's vote on a review node to count towards a product node?
The problem was that I had just switched the links between my Reviews -> Products to use entity relationships (instead of node links) and Fivestar does not support that.

A patch that seems to work was posted two days ago.  As soon as I applied the patch, the "target node" field appeared.  http://drupal.org/node/1488914

In addition, the product's Fivestar field had to be set to "rate while viewing" and the Review's Fivestar field had to be set to edit while eediting.