I tend to shy away from review exchanges, in the end it is an unlikely long term user and the rating is empty. I can understand the desire to boost your applications ranking for sure. It is a large store with many many apps released at a rapid pace, hard to get noticed.
The "rank my app" popup is a popular strategy but it is something you have to be careful with. It is important that it doesn't constantly appear like a nag screen to the user, it is also equally important that you wait an appropriate amount of time before showing it. I tend to set it up so that it won't appear until the user has had the app installed for a period of time, and the app has been launched a certain number of times. I find that I get more honest feedback from users who actually use the app.
it is also important to give the ability to dismiss the dialog forever, as well as a remind me later option that makes it go away for several launches. Getting ratings is important but not at the expense of your user's experience. When/how you launch the dialog is also important. if at all possible try and avoid interrupting the user experience, make it show at a time when the user has completed a task.
As far as rating exchanges go the problem I have with them is that they aren't real organic users, they are a fellow developer trying to also get ratings for their app. The liklihood that it will get rated and then immediately uninstalled is incredibly high.
The biggest way to get better/more ratings is to make an amazing app, nothing compels people more than a quality experience.
- MunkeeBonez