Hopefully this will be in celebration of the release of the first Map Pack for the PC as they still wait for the release. You should all give it a try though, Modern Warfare 3 on the PC has great graphics compared to the consoles if your system can handle it.
“Activision will be hosting a Free Weekend for Call of Duty®: Modern Warfare® 3! Pre-load the game now and be ready to play when the free weekend starts on Thursday, April 26th at 10am Pacific Time.
The Free Weekend of Call of Duty®: Modern Warfare® 3 will let you play the multiplayer portion of the base game.”