With a reduced TDP rating of 130W the i7 series is still very power hungry. The Q9 series is now available with 65W. If you think it's twice as fast, think again, because it's not. The normal Q9650 with 95W TDP is still the most efficient cpu.
Intel i7 975 is without a doubt the fastest desktop CPU in the world. The new stepping did not help to reduce the massive power requirements, but it was enough to maintain the title of the fastest CPU around. Overclocking is a bit disappointing as it is in the range of an Phenom II, but of course Intel does charge a fortune for their premium CPUs. The CPU is already available for about €860,- in Euroland, and about $1000 in US.
As long as you are not into photoshopping or rendering on a professional basis, there is no reason to go for this platform. If you need performance with balanced power-consumption the Core 2 Quad Q9 series are still the CPUs to go for. For less performance you can buy for the same cash a whole machine with an AMD CPU but still with an high end graphics card which would be a better thing if you play games.
If the money is not an issue, if you don't care about the Amazon rainforest and power consumption that will go even to sky high 334W and you want the fastest CPU / Platform money can buy, this is the CPU for you. Everyone else should reconsider.
Core i7 remains the fastest and the most expensive CPU around but it is very clear that Nehalem generation won't reach mainstream before Lynnfield quad-core comes out with P55 platform in Q3 this year.