This is pretty insane, Steam has broken another record for their concurrent user count hitting over 17.6 million. It was only in January that Steam passed 14 million concurrent users, so this is a pretty big growth.
Not only did they hit that allmighty figure, they also recorded 6.8 million users actually in-game, so not just people with Steam sat open doing nothing.
The thing is, it isn't just the sales driving this. It helps of course, as everyone scrambles to splurge the cash on the latest games, or whatever's been sat in their wishlist. On a day like today Steam is still sitting at around 12.3 million users, which is still extremely high considering the previous record.
I have no doubts that PLAYERUNKNOWN'S BATTLEGROUNDS is driving quite a bit of this, since it hit an all-time peak player count of 2.9 million around the same time. Honestly, if PUBG was on Linux, I would be playing it too. This is again a part of the reason why the Linux market-share on Steam has gone down (remember though, it doesn't actually mean less Linux gamers!), due to such popular games not supporting Linux and Steam's growth in markets where Linux isn't currently popular.
Now, just imagine how much money Valve is likely dealing with. Not just how much they're making, but how much passes through their systems every day—crazy! It shows how big a grip Valve holds on the PC gaming market and how far they could push Linux gaming in future once drivers have come further along, once VR support is better and so on.