I'm not sure how much dual-core will help. Dual-core will ONLY help if Apple has all those pro-apps (think FCP/Pshop) optimized for 4 cores by the time they are released.
People are disappointed b/c there is:
1) No new technology. DVD burners are cheap, those don't count. I'm talking about chipset improvements. I'm thinking on-die memory controller. Anything, just surprise us. Clockspeed "bumps" (where the price-tag on that new investment does not constitute a SUBSTANTIAL increase in performance) aren't enough now, especially if they can't even back a ridiculous promise by SJ.
But to put it simply, a band-aid "upgrade" just doesn't cut it. Marketing has their hands tied (spin a .2Ghz bump since the last upgrade cycle). Engineering apparently is going no where.
2) Prices remain high.
If Apple had released something new, something spectacular than it would be nice. We already know that Apple cannot use the "lower prices" trick b/c they would lose alot on the profit margins. Thankfully, they DID reduce the LCD costs, but considering the 20 and 23" models are on LCD tech that is over a year old, they'd better.