Notifications at the top-right, covering the top-right of whichever window is active. Fortunately most of them can be dismissed, but those concerning updates cannot, which is extremely annoying. I've once already accidentally triggered a 15 minute update, which can be extremely inconvenient when it happens at the wrong time.

I've found a way to get rid of the update notifications, though: click "details", which opens the app store with a list of your pending updates. As long as you leave that open, the notification won't reappear.

Still annoying, though.