I didnt say you would be.... but you do have 8 cores... and they all run at 3GHz... if you do the math... you have a total power of 24GHz under the hood. Which is not wrong.
No, it's incorrect.
You can make a comparison saying "If I harness eight identical horses together, they'll be able to run eight times as fast!" Except not. They won't be able to run any faster than a single horse would, they just might be able to pull more weight and maintain speed.
Running a properly threaded application that does not require any more CPU cycles than, let's say, 2 cores can handle, it will be no faster on an 8-core machine. Arguably, it will even be slower due to overhead created by communication between processing cores. However, when it becomes important is when using a heavily threaded application (Final Cut, etc. etc.) under duress, when having more workers available on the assembly line will speed up a complex operation.
There's a formula that explains this.
The statement above would be more correct, however with Peryn (or later?), when Intel has planned what is essentially the ability to combine multiple cores into one big core. In that case, you might actually be able to produce 24GHz of processing power in a straight line (probably less, given overhead) out of 8 3GHz cores. Not many details about that is known, however, but I'm sure it will become something of an industry standard across Intel/AMD chips in the future.
In short, I think 8-cores only has a performance increase for a very small set of users, given the same MHz measurement as an equivalent 4-core chip. If you need it, you definitely know. Most users will probably be better off using the same money they'd use on the 8-core upgrade on RAM.