Update: The new Nikon rebates are restricted to either the D300s or D700. Same with the SB-900 - in order to get the $100 rebate on the flash you must buy either a D300s or D700. I will have the full details next week (Adorama and B&H are close for a week).
I just got a confirmation that the Nikon rebate program is now extended till May 1st, 2010 (US only). Nikon SB-900 flash will also be included with a $100.00 instant rebate. My source also said that a new $300 rebate will be introduced with the new 16-35mm f/4 lens when purchased with the D700. Some new limitation on the rebate program will be introduced.
I will have the full details later today.