Often I see reviews such as "love the app but it's crashing sometimes since I upgraded to ICS 2 days ago, so I gave it 1 star". Don't get me wrong, it happened to me too on my iPad when I upgraded to iOS 6, but I simply sent an email to the developers, asking them whether a fix is going to come in the next day or two and they replied back promptly that I should wait for a fix later that day. The result of this interaction was a 4-star review and a happy user.
The sentiment of self-entitlement in some users is absolutely amazing, especially for free apps. I also see lots of reviews such as - "the app sucks because it displays ads and to get rid of ads you must pay". Well, if you're a cheap bastard, there's nothing wrong with that (I'm a cheap bastard too), but have the decency to stand up to your beliefs.
A negative review can really damage the reputation of an app. It can be used by your competition to lower your rankings and it can be used by bored people that have nothing to do other than to piss on the work of other people.
Anonymity has its place but I don't think it has a place in the app store. Many developers don't have the marketing budget of bigger companies, so they can't generate enough good reviews to bury the bad ones. Fake reviews are also harder to generate. This can't be bad for users.
And contrary to what other people say, nothing is going to stop me from posting bad reviews. I can stand for my own beliefs and I don't really care if my employer or anybody else thinks otherwise. If your app sucks I'm going to tell you so. If your app is mallware I'm going to go to extreme lengths to get it blacklisted.