Recently I am encountering this problem while using new Gmail: it randomly marks my emails as important, the ones I recently received from other email addresses. Not all emails are marked as important; say for example I received 3 emails, it'll mark 2 emails as important and it won't mark the 3rd one as important—I mean it picks any random new received email and marks it as important. Is there any logic behind this? Any idea why this happens and how can I stop it?
The official priority inbox video explains very clearly how it works.
Basically you need to teach to your Gmail how to recognise an important email to obtain a descent result.