As per the post at CallofDuty.com: To celebrate the continued success all of you have helped provide us with Map Pack 1 – and ever since the release of the game – we at Treyarch have decided to host a Double-XP MP Weekend for ALL PLATFORMS this weekend!
Whether you’re on the PS3, Xbox 360, PC, or the Wii; you will be accuring 2X the normal XP from Friday, 10:00AM PDT until Monday 10:00AM PDT.
Source: CallofDuty.com | JD on Twitter