Of course I review my own app. In addition, my co-founders review the app, my dad rates the app, my investors rate or review the app, and anyone else in the world I can get to rate or review it as well.
I don't consider that unethical in the slightest, considering my competitors literally hire PR firms to write reviews for them, and have armies of employees to do the same. I have written on this topic occasionally:
http://www.andrewljohnson.com/article/Fixing%20the%20App%20S...
It's not just that "everyone else is doing it" that makes it OK to do. If you want your star ratings to be in the same league as the rest of the apps on the store, then you have to generate more reviews than your regular users will provide to keep up with everyone else. It's not a matter of OK - it's a matter of survival.
I do wish there was more credibility to the reviews on the App Store, but that's just not the way it is. Maybe someday Apple's system won't demand all developers get all their buddies to buy and review their app. It's just absolutely pervasive - go check out some popular apps and see if you can pick out all the fake reviews. The clear giveaways are: 1) has only written one review, or only reviewed the app and competitors 2) references new features in the app 3) badmouths competitors 4) long and rambling. The fake reviews usually have some combination of these.
As long as the big guys are paying for reviews, I don't consider it even a little bit unethical to review my own app. Even in my little navigation market, the top app has a company and at least a dozen iPhones - that's a dozen automatic five star reviews. I can't compete on this front, but I can try.