I was just wondering how it is. Are we isolated in our own little GOG domain, or with Steam users. Just curious, thanks for the feedback.
DeadlyBuzz229 already answered that question. I'd like to add some info about my currently quite limited MP experience.
Not being much of an online player, I nonetheless left multiplayer enabled, but disabled player damage, and add / delete base parts. No interest in PvP, or having others have a creative go at what I built :)
I have to say, that for now I'm quite pleasantly surprised. I've had starters being a bit lost asking for hints / help, more veteran players blasting by leaving a quick hello, got shown some nice planets and loot, taxied people around in my freighter and lend out Exocrafts and other equipment.
As far as I can tell, other than harvesting crops, other players can't change a thing at my base or freighter, if they join my game. Also, players don't take damage from each other whatsoever, neither do their ships.
The environment will be the same for all players, apart from from weather effects -- storms are local to each player. I have yet to find out about the exact differences -- e.g. if animal and loot spawns also are completely local to each player, space battles, etc. Edit: Animal and resource spawns seem to be synched, and not local to each player. Edit: Space fights seem to be shared, and it looks like all players involved get a rep up for kicking around pirates. Some of the sound effects also seem to be shared via the intercom, e.g. the countdown once scanning commences, or a players' ship being hit, but not the voice warnings.
If a player aggros the Sentinels, they'll only aim in on the offender. I've stood right next to someone shooting down Sentintels in a row, and got completely ignored. But then, I didn't really try and get the buggers cams aimed in on me by e.g. jumping in front of them.
You can taxi other players in your freighter. They'll stay in the exact same position -- if a player's on the bridge before the jump, he'll be on the bridge after it. If you call your freighter to some position while another player is on board, he'll be put back into his ship aboard the freighter.
As with all non-owned freighters, no save point is created, when another player exits his ship on your freighter.
If you build an Exocraft Bay, other players can use it as if it was their own, calling their own exocrafts, without even having the blueprint for that particular bay. Same for refineries, though the inventory is not shared. In my game, other players can not access my base containers. They can, however, access the freighter storage rooms, but seem to get their own 'copies', not being able to see what I put in there.
If you join a game, and then reload your your normal save, you'll retain all inventory items and ships gained, including new teleport locations learned, but will be put back into the star system of your normal save. There seems to be a nasty bug with that, if you're in a different galaxy than the player whose game you joined, but since I'm still in in Euclid, I wasn't able to verify that.
Finally, the 'orb or not orb' thing ... in my experience, if someone jumps into your system or the game randomly spawns them there for starting, they'll be an orb. If they join your game by using 'join random game' or by accepting an invitation, then you'll see their model, their ship and anything else.
All in all, I think I saw about 10 other players over the last three or four days. Some of them even started in my system, or at least died trying. Funny enough, they all started at the same spot. I've finally put a beacon there, so people can at least do a hard save -- and realize, they're not alone.
Seeing another player getting airborne for the first time, after he's fought his way through what you went through yourself is really quite something. I'd really love to be able to hand out beers, hot tea, cold lemonade or whatever in my freighter for celebrating their survival of the hardest part of the game :)
Uh. Well. That was a bit more than what you asked for. But I've not seen any definitive explanation of the multiplayer part yet, so I thought I'd add what I currently think I know about it for those hesitant to try MP.
As someone, who never missed MP in NMS, I'm glad I tried it. It really can add to the experience.