I am in a similar position. My applications are complete and the LSAC reports have been sent to USC, UCLA, & UC Hastings. However, I have yet to receive a decision from any of them. I believe they do not have to reply by April 1. They could decide to contact me in August if they choose to.
Sending a nasty letter may give you an outlet for your anxiety & anger, and would definitely result in a negative reaction from the schools. There is absolutely no reason in the world to do this to yourself.
Be patient & cope with the stress in a constructive manner. I understand your pain because a lot of us here are in the same boat.
Best of luck to you.