Announcement 1, SteamOS: is just a fancy way to say you can create custom Steam consoles by just installing some software. Make the box as good or a cheap as you want and everything will just workPretty awesome, but definitely this will be dwarfed by...
Announcement 2, people are guessing is a Valve distributed "SteamBox": a console that is presumably very cheap and linux based. This would give Xbox One and PS4 a run for their money and with the social aspects of Steam built-in, this could be a break out hit with a price of 50% all the other consoles.
Announcement 3, is the large unknown here. We don't know what it is, but if it is bigger (or equal to) SteamBox this could be a huge deal. Nothing really makes sense here. We know:
* SteamBox will support streaming from your windows/mac machine so it will be able to run every game at launch.
* SteamBox will likely have lots of publishers signed on. Probably as many or more then on xbox one / ps4. If they are already using an engine that targets multiple platforms (Unreal or Unity) they are definitely going to try to support it.
* SteamBox will likely support all the features of steam with friend lists, chat, voice, purchasing over the cloud, etc. So the + might mean sharing, but a new kind?
* SteamBox supports game sharing at a friends or family level. I see this as a kind of Netflix-like persona idea: an account gains separate personas that each have different friends lists and achievements. Very powerful and necessary once Steam hits the living room and multiple people are using the same box / account.
What it could be:
* LAN play for SteamBoxs on the same network (announced in Dota, this could explain the circle + circle graphic). Maybe you share the game between friends, and stream to the other boxes? That would be pretty awesome.
* Game streaming from other people's SteamBoxs? This would be an awesome way to share a game. It is like onlive but for distributed for everyone (seems unlikely. That kind of streaming would stop your friends from being able to play).
* A launch title like Half-life 3 (seems unlikely with the circle + circle logo implying you need multiple SteamOS instances).
* A new kind of social experience, maybe a built in way to be a part of the game creation process or improved social network experiences on Steam (seems unlikely to be big enough to be the final announcement)
* A new kind of hardware like a VR headset(seems unlikely, as cheap will be a big feature of this box)
This is marketing at its best. They hooked us good.