The Aperture Labs Countdown timer has concluded, and while this does not signal the launch of Portal 2 as hoped, it does seem to indicate an early launch is possible, but it requires more "computing power." The page now offers a new "projected launch" timer, reading a bit under 94 hours, which calculates out to Tuesday, but from the looks of it, this process can be sped up through The Potato Sack games, with a note at the bottom labeled "challenge status," next to an unexplained potato multiplier. Here's the message that precedes the new page loading:

09:00 – Hello again.
09:00 – I’ve been waiting a long time for this.
09:00 – I know it’s arriving later than expected.
09:00 – But I have a message for you:
09:00 – April Fools.
09:01 – I’m joking.
09:01 – Seriously, though:
09:01 – You’ve been surprisingly competent at
09:01 – generating electro-chemical energy to jumpstart the system.
09:01 – But now we need raw computational power
09:02 – to speed up the reboot process.