Disclaimer: Most of the comments so far are from ATI fan boys, so I will attempt to equalize the scale a little bit, so don't throw any *snappy* comebacks at me... they are not required.
Since there are absolutely no DX11 games out there, and there are DX10 cards that can play almost all current games (except Crysis - which somehow I've managed to play on my GeForce Go 7900GS tucked somewhere in my Inspiron), I don't see why you'll want to rush over and buy expensive ATI/AMD gear.
And if in this tech demo, the GT300 is more powerful then what ATI has to offer, then I really can't see why you won't wait... unless you have ATI stamped on you brain... ATI is making a simple incremental upgrade of their existing technology, essentially upping the number of the SPUs, and doubling the ROPs... a big mistake on ATI's part, the number of ROPs should've been increased ages ago. On the other hand nVidia is changing a lot of things in it's core design, switching from SIMD to MIMD and adding DDR5 (I know ATI has it already, but nVidia will *presumably* have more bandwidth as a result of a wider bus). Their only problem is that they are keeping the monolithic design of the GPU, and this translates into higher production costs then ATI has to deal with.
So when you see an ATI card that performs the same as an nVidia card as the same price, you should know that ATI makes more money then nVidia does. So it is questionable about who is screwing who over. So far nVidia has to cope with very high production costs of the PCB because of wide bus DDR3 implementation, and the presence of the NVIO chip. Hopefully switching to DDR5 will make the PCB a lot simpler and cheaper for nVidia to manufacture and maybe it will have a fighting chance on the price front.
I see people thinking that RV870 will be hard-launched in September. It will be hard launched in December actually, on the 10th. Repeat after me... September paper launch, December = hard launch. Buying at launch always hurts your wallet. You can repeat that 100 times.
If you own a GTX275 or a HD4890 or better card, buying into this ATI DX11 hype now will hurt later, when prices drop and there are actually DX11 games worth playing. If you have a GTX260 SLI or a 4870/90 CF setup then you're making the biggest mistake of your life.
If you are made of money, if you have rich parents and they spoil you, if you've inherited a large sum of cache, if the banking system made an error in your favor, ignore what I said and just buy the damn thing, so we can all have benchmarks to compare our hopefully better GT300 cards with.
Take it easy, life is hard, don't just kill me yet, wait 9 months, see how it goes.