FUD Zilla claims a dual-GPU version of the GF100 "Fermi" GPU may follow roughly one month after the launch of the single-chip card:
Single-chip Fermi and the card codenamed GF100 should launch in March. This should be the launch time frame and a dual-chip version might follow in roughly one+ months after the official single-chip launches.
This is roughly the plan as it will take some time to prepare this dual headed beast, especially since Fermi will be the hottest chip in Nvidia's history. Naturally, putting two such chips on the same card won't be a walk in the park.