OK, so maybe I haven't covered the following enough. To writers looking for agents or publishers, please carefully consider the following:
The publishing world is smaller than you think. Curse out a publisher or agent for rejecting you and word will spread. If you are angered by getting rejected, vent with your friends in conversation. Never write back and curse the publisher/agent out, and NEVER write nasty blog entries trashing them. To make it easier to forget a rejection consider that:
1) The rejection may simply be because that publisher/agent has already published similar stories recently and wants to go in a new direction
2) The rejection may simply be due to the fact that the publisher/agent has too many clients at the time to sufficiently market your book
3) The rejection may simply mean the publisher/agent didn't really enjoy your story and doesn't believe she or he can provide the enthusiasm your deserve from an agent/publisher.
Rejection is nothing personal. If your manuscript is rejected, take time to consider any reasons stated for the rejection (if any) and move on. Trashing a publisher or agent in a tirade over the phone, thru an email or on a blog won't likely help you sell the story to the person that rejected you. But, such a venting of your frustration may get your name out to other publsihers/agents, who will possibly ignore all your submissions.