1. NVIDIA promised double precision floating point in the end of 2007 to the developers.
2. NVIDIA needs new high-end part with lower power consumption (read single slot cards) so it can revive SLI and Quad-SLI interest.
3. NVIDIA needs DX10.1 compliant chips and GDDR4.
4. NVIDIA would f*ck up ATI completely if they manage to release another high-end chip
Based on that, I believe that there will be new high-end part this year.
We already have enough low end parts and they never start with releasing low end. High-end comes out first. Furthermore, if they launch in the same time frame as Intel (Harpertown in November) AMD will be between a rock and a hard place with no answer on both fronts and their shares would go down.