The nine 'test subjects' are nine of the main ARG participants from the beginning of the event. Their diligence, and central location, has earned them access to 'test' Portal2 at Valve's offices. A good deal of the ARG was centered in Seattle, meaning that the main respondents would be Seattle residents, and therefore close to Valve's main offices.
A small part of me seethes at missing this oppotunity, simply because of geography, but the rest of me beams at the idea that a developer (and their marketing team) can come up with such an ingenious and engaging plan to, not only draw attention, but also impact the sales of several 'indie'* developers. I, for one, did not get drawn in by the Potato Sack 75%-off sale (only 3 or 4 games realy interrested me, overall), but I know that they surely had more than a few purchasers because of this stunt.
I'm pretty sure that the Steam release of Portal2 has been refined and essentially set for release more than a few days, so having the release time be shortened by ~10 hours has no real impact on Valve or their servers. Actually, I would expect that they were ready for a 12 hour cut, but maybe didn't expect more than 8 hours to be taken off of the original release time. Only through massive community cooperation to clear games off of the list(required "CPU Calculations" appear based on total game sales, not merely some arbitrary round number, hense the popular titles have required more players logged in and playing to further the bar's movement) has so much progress been made.
*: For me, the term "indie" has lost it's luster. They are all "developers", some are corporate-based, some are not. Just because you are one, or the other, does not bestow any special place in my judgement. The game is either to my liking, or not. Within my playstyle, or not. AAA; Indie... what does it matter, if I don't want to play it?
Captcha: from tertY
It must be true, if tertY says it, right? Heheheh.
Edit: Addendum
Currently shows 82 Test Subject online... and ~1hr left until reboot.