I've seen a bit of confusion in various articles and some blogs about the application id, and I wanted to take the time to clear up a popular misconception:
Your application id has absolutely nothing to do with rate limiting. Your IP address has *everything* to do with rate limiting.
Getting yourself another id will not allow you to get more queries. The application id is for self-identification, to help you get some basic usage tracking and to let us get in touch with you if one of your applications has a bug that needs fixing. That's it. Think of it like the User-Agent string a browser sends out.
So, the next time you read something that says "per application id," ignore it. If you have suggestions as to how we could make this clearer, we'd love to hear them in the comments.