Well, SI are launching two new gameworlds today, which is good for the 2000 people that have already got in on a first-come-first-served basis to fill them up.
Those guys should be getting an email from SI today I guess, telling them what time launch is and where to get the client. For me, this is likely to be the biggest stress test - it's going to be pretty effectively modelling the retail environment, where a world is filled and launched, and everyone tries to get online at once to sign their initial squads.
How the servers cope with this will, in my opinion, be the determining factor in the launch of the game. There will of course be further improvements to the code to be made, but if things go well I reckon these guys will only have 1 season in the beta... If things don't go well - fine, SI make the improvements and maybe that takes a little longer.
For me, I think (and hope!) things will go well... Good luck to SI, and to all our new members in the testing community!
I nearly forgot - a lot of the new guys are planning to write FML blogs, so you can keep up with the latest additions to the FML blogfest on the official forums.