I was inspired by this post that I found through Elizabeth Craig on Twitter, a fantastic one called "When Going Green's Not So Cool: A Writer's Antidotes for Envy". My favorite antidotes were: enjoying the things you love, and exercising. I highly recommend those for all writers, especially since a lot of us (including me) need to exercise more.
I personally find that I'm not immune to jealousy, but that my jealousy is rather limited in scope. My jealousy will make me feel upset at myself, but not angry with others (I feel lucky about this). Even when I notice a bestseller whose work I don't particularly like, I figure that person has found something that a lot of people like - I just may not have grasped what that thing is.
The other thing I continue to believe is that writing is not a competition. It's not about whether my writing is better than someone else's. It's not about two writers with similar styles trying to fit into the same too-small market niche. It's simply about whether I find an editor who finds that my work speaks to him/her, and whether readers then are willing to pay for what I do. Honestly - why should I worry about whether I'm similar to my favorite authors? When I read, I don't say, "Ursula LeGuin is my sf author, and there isn't room for anyone else." The more someone's work is like hers, the more likely I will enjoy it too. Reading appetite is not finite. Reading quality work does not satiate; it only makes you hungrier for more brilliance.
The last thing I hope writers will remember is that statistics only operate effectively on large numbers. The fact that 99% of submissions get rejected at a particular magazine should not deter you; whether your story succeeds is about your story, and that editor, and it has nothing to do with anyone else.
Keep up hope, and keep submitting. So long as there are readers hungry for stories, there is room for more authors.