Bad news: If you're hoping to get a Steam Machine this fall, you're going to have to wait until the official release date of November 10 like some sort of plebe. Valve announced today the entire stock of "Get it Early"--a.k.a. "Get it in October"--Steam Machines is sold out. And they sold out in less than a month! Pop that champagne, Valve.
Or pop some champagne, at least. There's a big question in all of this, which is: How many machines have sold? We don't know, so this is a bit of a PR stunt on Valve's part. For all we know, the October allotment of Steam Machines was a hundred units. Or it was a billion units. It's good news for Valve/Linux fans either way, but how good? That's impossible to tell.
Further reading: Steam Machines revealed: Full details and pictures for every model
There's also the question of why supply was limited in the first place. I'm going to guess/wildly speculate that aside from the SteamOS operating system itself, it's the Steam Controller that's the manufacturing bottleneck in this whole process, considering the other two bits of hardware are quite a bit simpler--the Alienware Steam Machine is basically just a rebranded Alienware Alpha, and the Steam Link is I assume just a collection of fairly standard parts.
If the Steam Controller is limited, I have to wonder how many Valve's managed to stockpile ahead of launch. Are we going to see the November preorders sell out within the next few months? Because that would be a pretty big slap in the face to naysayers.
Regardless, you've officially missed your chance to be an "Early-Early Adopter." At best, you'll have to settle for just "Normal Early Adopter" which isn't quite as cool.