Call up a dealership and ask what the most you can pull and just stay under that.
This is just not true. There are other factors.
There will be max tongue weight (100lbs as said above)
Max Trailer Weight (1000lbs as said above)
and Max Gross Vehicle weigth... Trailer, Car, Passengers, luggage, amount of fuel, and other things. Remember that you car has a dry weight rating.
I have seen many wrecks in this are due to people towing what their vehicle can pull. Its not about being able to pull, its about controllign it when you get on the roadways. Too much crazy crap happens that you cant be prepared for because you are relying on anticipating wha other drivers will do.
I live in a heavy boating area, and you should see what some of these clowns do. Then what happens when someone with a car tries to pull a 5000lb boat.