I'm quite proud of the fact that I always try to provide the best app support. That means that I answer basically all emails and I even go as far as to find users which rated the app on the App Store and contact them, if the issue seems important.
And that's where it's a little bit tricky. John Gruber, after releasing first iOS app with some friends, recently decided to share his thoughts about rating apps on the App Store (from a perspective of a person which doesn't really need reviews). He's apparently is very annoyed by occasional popups that asks users to rate the app. To the point that he encourages his audience to rate those apps with one star. Mature.
The problem here is that the App Store rating/review system is flawed. First of all - if you don't encourage people to rate your app - you (almost) get no reviews at all. The way people use their devices and apps doesn't support that behavior. It's more and more difficult to find a good app on the App Store, which fits your needs. Which leads to the fact that after checking several apps, people are usually tired of the whole experience and don't want to go to the App Store to leave a review. If they do, it's usually not a nice one, because for some reason the app didn't work as they expected it to work. If the app is fine, they usually leave it for later, telling themselves that they will rate the app if they'll use it after few days. Which of course they (almost) never do. Unless you show a popup from time to time, to ask for the review. It's not an easy task - if you'll show it too soon, you'll never get a review or get one star from John. If you'll show it too late, the person can be busy, too use to the app etc. With just the right timing the person will be excited enough that he/found the "perfect" app after long search, and will express that positive feelings the review.
Now there's another side of this story. There are people out there which uses App Store reviews as a way to reach the support, to say they have problems with the app. Those are most useless reviews there are. Not because they change the way people look at the app, since most of those describe only negative aspects of the app, complaining about bug which happens ones every 100 runs, forgetting about great 99 bug-less experiences. No - I think we can handle that part quite well, making sure there are least bugs possible. The problem is that there's no way for us - developers - to respond. If you have a problem, we want to reach you, we want to get as much information about your problem as possible, to fix the app for you and others.
If you'll leave a review, all we get (assuming we get those reviews somehow) is your very short explanation that something's not working, 1-5 stars and your name. We can't respond to that review, explaining what's happening, saying that we already know about the bug and maybe even already fixed it in the newest update. We can't contact you to, to ask about the details, to give you a promo code for one of our apps, as a thank you for mature review, instead of 1-star rage fest. Those reviews are for other users, and I would even say that they are pretty useless for them as well. You can say that app is bad if it has 90% of 1-star reviews, similar with 90% 5-stars, but with everything in between is not that simple anymore. As a result you won't get that problem fixed, you won't get kind e-mail from us where we could explain/thank/help you. You'll get us read your review and know that one from couple of hundred millions of potential users has a problem. That's it. Even if we really wanted to help (which we usually do), there's just no real way to do it. Even if we would try to to always actively search for you, you're not the only John Smith (or johns16) on the internet and it's infinitely easier to find a way to contact the app support, than harass random Johns on Facebook or Twitter, cause maybe they left that comment on the App Store.