Either a temporal anomaly has disrupted Valve Time, or Valve has just been very busy. Not only has it announced and launched Team Fortress 2's Mann vs. Machine mode and the closed beta of a big Steam community update , it's updated Portal 2's free Perpetual Testing Initiative with support for co-op puzzle creation and a new Quick Play feature.
In addition, current owners of Portal 2 will receive 75% off Portal 2 coupons to share with friends. The coupon isn't in my Steam inventory, but others are reporting that they've found it, so have a look. If all of your friends already own Portal 2, why not check to see if any sad, Portal 2-less souls are hanging out in our Steam group ?