It would be great if arbitrary fields could be set to display from stars. Here's the idea: under the custom library field dialog (or non-custom), there could be a simple drop-down or checkbox for rating.
The reason I say drop-down is because I would like even more a second option. One that would, if using integers with values, could have almost like a bar graph in a field. Take a field about 1/2 the size of the rating field width and then add either a vertical or horizontal fill-up based on the value divided by the largest value.
More complicated would be handy here: Take another box, perhaps 1/3 the size or less of rating. If the value was 1-2, it would be empty. For 3, it would be a small circle. For 4 or 5, a much larger circle. For an easy way to specify this, you could use under the values box 1=>0; 2=>0; 3=>1; 4=>2; 5=>2. That would be a reasonable way to essentially re-write the categories value to a more simplified value that could be displayed, either via 2 stars (0,1,2). This would help keep the new field small (width-wise).