Nehalem will all have Turbo Mode

The Penryn processors for portables can run one core in overclocked mode at a higher frequency if the other core is not being used. The goal is to offer a little additional power for applications that do not support multiple processors.
Intel will extend this function to all the Nehalem processors, whether they are intended for portables or office machines.
In fact, if a processor with 4 cores is running with only one or two in use, these will increase in frequency by a little less than 10%. The power can not exceed maximum thermal envelope defined for the complete CPU.
Since this all will be managed in a transparent way and without any risk, this additional power is always good to have, especially on of Mac Pro equipped with 8 cores where the majority pass a good part of their time doing nothing.