If I am the BUYER, I do NOT LEAVE FEEDBACK FIRST. Ever. I will send the seller an email acknowledging receipt and expressing my satisfaction/dissatisfaction regarding the purchase, but feedback will be left after the seller has left feedback for me.
I don't do this to be ugly, but because frequently sellers require that you leave feedback first, and then don't ever get around to posting return feedback.
I believe that we here on EBay need to be fair and honest, and I make every effort to clearly state and resolve any issues in a transaction so that there is no need for feedback war. You can check my feedback to verify this, I have never left or gotten a negative, and I hope that I never will.