Messages.app gets cross-device notifications just right

TL;DR:

When typing in Messages.app, iCloud knows your in Messages.app. When typing on the iPad, iCloud knows your on the iPad. When you're engaged in a conversation on one device, the other devices do not get notified of new messages. This avoids cross-device notification flares currently experienced by calendar alerts, which makes for an especially noisey 9:55 AM for me.

Now say you're working, working, working and Messages.app is out of focus. At this point, iCloud doesn't know what you're up to. A new message comes in. Since iCloud doesn't know what you've done since the conversation stopped it notifies all your devices.

You're still in OS X so you reply to the message via Messages.app. Now you've got notifications to dismiss on your iOS devices, right? Total first-world bummer, right? Nope: iCloud dismisses the notifications across devices once the conversation picks up again.

No extra X-ing out of things. No burnt seconds of your life. Just gets rid of them because it knows you've started talking again.