Preferences ==> Interface ==> Behavior
Uncheck "Show notification when new version is available".
There should also be a checkbox in the actual alert popup.
Many people -- perhaps most of calibre users -- only update when there is an update they need. There is no need to update every week.
For those who like to update anyway, and pay attention to the presence of updates, the weekly release cycle allows us to take advantage of new features as they are released. It also means new users start with the latest stable code. Kind of like Firefox Nightly except more stable.
