So, for all that I hate them, what's good about a utopia / dystopia?
1. They're a pain to write well. A well written one needs research to be plausible and it can be fascinating to see what the author knows and how well they can explain it. A challenge can be fun.
2. A lot of 'normal' plots have trouble working in utopias/dystopias. Therefore, the author may be able to stretch their writing skills in not just making the place believable, but also making it intersting as more than a clever world.
3. They're a good way to attack or talk about things that may be hard to write in a more real-world plot.
4. Sick of sunshine and light or sick of gloom and angst? A utopic world could let you have your happiness and a dystopic world could let you have things decay to your heart's content.
5. As world building excersizes, they're great fun. You're juggling how much you want the world to be diversified to how much you want your utopia/dystopia to be world wide. You're juggling having enough without too much information. You're juggling believeability. You're juggling how utopic / dystopic your characters are. And, on top of all that, you still need the nuts and bolts of names and places and a plot.
So, how can you fix what I hate?
1. Characters. Write well done 3D characters. Personally, I find totally shining perfect characters and totally imperfect characters to both be unbelieveable. Therefore, you have to juggle the goodness/badness of your world with how this world affected your people. You also need to make sure that your main characters are not so alien so as to be ciphers. Make sure they're internally consistant. For example, I read a 70's era feminist story wherein storytellers were supposedly one of the most respected people in the society. However, because the storyteller wasn't as active and angry as one of the other characters, the author wrote the storyteller as being ignored. This was not internally consistant with the world, what the people claimed to want, or the characters.
2. Research. Decide how realistic your world will be and research to make sure the facts line up with this level of realism.
3. Plot. Make sure your plot is plausible in this world. Is it compelling? What is your focus? Are you forced to bring in outside forces for conflict? If so, what does that say about the world? Be carefull of having barbarians bringing in trouble, since you can end up with racist overtones. Also, be carefull that your utopia doesn't seem like the barbaric ones by accident.
4. Politics. If you have a didactic or political aim, is it persuasive to both your side and the other? Is it well written and logical? Have you checked for class / race / gender etc. biases that you may not be aware of?
5. Novelty. If this is yet another dsytopia ran by 'Big Business', what's novel about your world? Why should I, the reader, care? If your plot is primarily exploring it, how are you pitching the world to your audience? Is it interesting to multiple groups or only one? Is it novel to your audience or phrased so someone unfamiliar to the concept might be intrigued?
Why are these problems prevelant? Well, I think part of it is that people don't question their ideas of good and bad. If your idea of a perfect world has all the women beautiful and flirting with you, then there's issues there with gender equality and sexual freedom. Also, there's the problem that if you say a world is perfect, but want to have plots with, say, murder mysteries, you've got a conflict of your stated 'perfection' and your plot goals. If you cop out and have outsiders show up to murder people, you've got the problem that you're instantly placing outsiders as barbarians. You can't really have another utopia meet your utopia since your plot (unless if the utopic ideals clash in a way that results in death) won't work.