Even though DX11 isn't widely used yet (how could it be, when DX11-capable cards only became widely available this month? (Widely referring to plentiful and cheap mid-range parts)
On the other hand, even without DX11 the 5xx0-series pretty much own everything else on the market right now. Previous gen cards are already a hard sell and getting worse as 5xx0 prices are starting to go down.
Fermi right now is set for a spectular FX 5800 Ultra-level failure: late, expensive, power-hungry and potentially underperforming in actual games. Nvidia's slides say that Fermi wins 5870 by 60% in Unigine/tesselation, which is impressive - until you realize that they are comparing a potential $600 card (Fermi) to a $350 card. In other words (speculation):
(a) there's a good chance that Ati's 5970 is very close or faster than Fermi.
(b) the difference is likely to be lower than 60% in actual games (this is a tech demo showcasing a very specific part of the pipeline - actual games tend to be more balanced in performance)
(c) Fermi may be launched at a lower price than previous Nvidia high-end parts (typically $600-$700). With a little luck, it Fermi might go down to ~$500 - still pricey, but a much better value proposition given the 60% (max) performance delta.
One of the links posted here mentions a late March launch date. Come on Nvidia, we need some competition here!