Your ratings are valuable even if your contribution is not immediately evident. Please consider the following:
Consider this example. If five people rated a message, each giving it 3 stars, its current rating would be 3. If you then rated the message 4 stars, your single rating would not have enough weight to move the overall rating from 3 to 4 stars. However, if other members give 4 or 5 star ratings, their ratings in combination with yours, could eventually make the difference and improve the overall rating for that message.
Please also make sure that when you give a rating, you are clicking the scale below the message. To rate a message, mouse over the grey stars that appear just below the message text. As you do so, they turn red and display the label showing what each star represents. When you decide on the rating you want to give, click a star and a button to save your rating appears. You cannot change your rating after it has been saved.