I thought that Merom chips were supposed to run in the range of 8% better at the same power consumption and clock speed. I might be wrong, but that makes more sense to me than a massive 20-30% performance increase all of a sudden.
As far as Apple's line later this year, I agree with everything Dave says and want to add that I think the Core Duo is staying in the MacBook for a nice long while. As soon as Merom comes out, they'll shove that guy in the MacBook Pro and probably even out the features between the 15' and 17' (15 will get a DL burner, hopefully firewire 800, the right-clicking trackpad, etc.)