Well, I'm quite curious.
I have a 2Gig of RAM in my macbook core duo, and have just put a 250GB HD in it.

I have noticed quite a lag now with Leopard installed. Safari constantly beachballs. And apps take seemingly longer to load.
I am putting alot of raw image files through it, and running memory hogging safari and Lightroom together slows the machine down to a crawl.

So I am wondering, is a 2.4GHz macbook with 4Gig of RAM really noticeably quicker? For that matter, is a 3.06GHz iMac?

Could it be akin to a comparison between my old powerbook 1.25 to the macbook core duo 2GHz in terms of speed?

Let me know what you think or have experienced?

The newer ones as you've mentioned can do 4GB, twice as much as the Core Duo ceiling.

They also run at faster bus speeds, from your 667MHz to 1066MHz.

So yes, I would say it is a big leap forward as I have gone from a Core Duo MacBook, 2GHz, same as yours (Mid 2006) and went to a 2.4GHz iMac with 4GB.

Big improvement.

3.06 will be even better. I'll just have a guess and say 2-3X the improvement.

Don't forget the unbelievable jump in Graphics performance. I know they really are just numbers and the truth is it often doesn't match but Engadget is getting 10x over a slightly newer MacBook in the Graphics Department.