Prices of the 5D2 have started to creep down. Because of that I decided a month ago to exchange my old 30D for a new 5D2 and I'm happy with that decision.
Before that I had decided I wanted the 1Ds3 or its replacement, but after being invited to the Canon promo event for the 1Dx & listening to the comments being made about the 1Ds line, I made a decision in favour of the 5D2.
Yes, it's always going to be the case that rumours will circulate about the "next" camera, but be realistic, how long are you prepared to wait and will a 5D3 be what you wanted when it does eventually appear? I'm a great believer in the old saying "A bird in the hand is worth more than two in the bush".
Rather than wait for a fictional 5d3, have a careful look at the 5D2 compared to a used 1Ds3. The latter will flood the market when the 1Dx is released and while in theory it is the same 21.1MP, the sensor and processor are in fact different & allegedly better.