My experience so far has been OOF is buggy. As Michael says, the OOF updates on some form of a Timer that isn't consistent and needs some work, but the fact it works at all makes me happy. You set your Out of Office message in Outlook to activate, but it takes up to 30 minutes it seems to change your status on and or off, once it's set you can't manually change the status, you have to deactivate OOF and wait for whatever changes it to happen in the background.
Also to add to this, if you book Meetings in your calendar with "Show as: Out of Office" on the meeting you will show out of office status with no message just a status.
The new contact groups could be better if the default of what you clicked saved, so when you click chat tab the Contact group view came up by default instead of recents.
Seems they changed the way Out of office works when @mentioning, it used to say who wouldn't get the message cause they were OOF, seems to just show a number of people getting it, which is the number of people in the Team minus the OOF folks.
You can hover over Channel mentions now to see how many favorite the channel, I wish they never removed this count from the Manage Teams > Channels view, not sure why the did?
However, one huge improvement has been no more random "unknown Status" for other Teams users and presence delays. When you set a status it instantly now changes, and if you pick busy etc. will stay busy and not revert to available like before.
Overall a huge step in a positive direction, but I'm sure the bugs will be worked out..
Also another note, to tell if you have it, you will get pushed version 1.1.00.14359 of the client as well.