There is another upcoming freeweekend with X2 exp apparently
according to the steam powered news site

Quote
'All News
FULL STORIES HEADLINES
16:34Call of Duty: Modern Warfare 2 - Preload Now for the Upcoming Free Weekend!
Announcement - Valve
Now's the time to get your Call of Duty: Modern Warfare 2 ready for the upcoming free weekend. This weekend will feature double XP as well so don't miss out. If you already have Steam installed you can click here to start the preload. If you don't have Steam, you can download it here.'