The official City of Heroes site updated today with an announcement for the upcoming weekend:
It's an exciting new year. Paragon City™ and the Rogue Isles™ are buzzing because the time is coming once again. Roughly twice a year we turn up the dial and invite players to rack up XP at double the normal rate. For an entire weekend, Hero and Villain characters will receive double the XP, Prestige, Influence, and Infamy for all of their accomplishments in the game.
The fun begins Friday, February 8, 2008! Take advantage of this opportunity to level up your favorite Heroes and Villains twice as quickly as normal. Good luck and have fun!
Double XP Event Timing:
Start: Friday, February 8, 2008 at 8:59am PST / 11:59am EST
Finish: Sunday, February 10, 2008 at 8:59pm PST / 11:59pm EST
Check out the rest of the details at the link above.