Todays rumor is a small one, and comes off of 40konline via Dark_Zadok. Take it as you will with a lot of salt.
I hear from a reliable source amongst Game Workshop:
All Game Workshop Managers have been told to Pencil in Necrons release in July 2011.
Please note: "Pencil in" means this could be subject to change, but does provide Necron players with some hope of seeing their Tombs rise this year.