The last rejection I got came from an agent I had met at a conference and who had shown a great deal of interest in my book. Her rejection note had this line in it: "I've had a chance to read the excerpt you provided, and while there were interesting aspects to it, I'm sorry to say that wasn't drawn into the story in the way I had hoped to be."
Not the worst thing that has been said about my book and I'm sure it was meant in a very friendly way. However, I can't help but see it as a back-handed criticism--she liked the concept well enough, but was disappointed with my execution.
And even if she meant no harm, as I'm fairly certain that she did not, I can't help reading more into, not when my heart's work is so involved.