The successor to Nvidia’s Fermi architecture, a certain GPU that goes by the name Kepler has already been taped out.
We have multiple sources to confirm that the new 28nm chip is alive and that it looks quite well. Nvidia didn't have any major obstacles with the first tape out, but naturally there is still a lot of work to seal the leakage, and make the chip generally better. This is nothing unusual for a new chip, and getting from 40nm to 28nm is definitely not a walk in a park.
Kepler naturally gets a lot of changes to Nvidia's GPU and you can imagine that with the same maximal TDP, you can squeeze significantly more transistor and get much more power.
The optimistic projection is to see Kepler in retail in Q4 2011 but some sources suggest that this won't actually happen this year, as TSMC needs a bit more time to make the 28nm more mature.
Current generation GPUs are already hitting the performance wall at 40nm and the industry has a lot riding on the 28nm process, but fear not. For the moment, both AMD and Nvidia seem to be on track and we might see the first 28nm chips by the end of the year, but mass availability comes a bit later.