I use one star to indicate that I have worked on the image. If the image was no good then I would not have worked on it and if I did but it did not turn out OK, I would not rate it.
Other than that, I don't use stars for permanent rating. What seems stupendous to me today looks ordinary next week, so I would just have to change the rating if I rated it today.
I use the stars for temporarily culling the best of similar images. I compare two images, the best gets two stars, the other is left at one star. Then I compare the two star to another similar one star image. If the new image is better it gets two stars and the original two star is demoted to one star. Repeat until all similar images have been compared and there is one two star 'King' left. I keep all of these images, the crap has already been flagged and deleted.
As to my best images, they don't need a high star rating - their location is searingly burned into my brain as there are so few of them. And if I forget, I have keyworded extensively so that they are easy to find.
Another use for stars is in collections to keep track of images that have been submitted to a physical gallery. I have a hierarchical structure for gallery images. One folder is for 'candidates' - those to yet be printed. After printing, the image is moved to the 'printed folder'. It is then matted and inventoried but still in my possession. When this is done, the image is moved to the 'Gallery' folder with zero stars. This means that I still have the image but it is ready to be delivered. When the image is delivered, I rate it as three stars. If it is sold but I have not replaced the sold copy to the gallery, then I give it four stars. When I replace the sold copy, I rate it as 5 stars.
This takes a lot of work and you have to keep it up to date but it is the only way I could think of to initially keep track of the images. I have to set up a database or spreadsheet for more complete information entry - for example the collection will let me know if it is sold but how many copies? If you know of a good commercial or shareware application that is good for this let me know.