Notebooks of today simply cant handle quad core. Have you EVER seen a notebook with a quad core?
Maybe, eventually, someone will develop an advanced cooling system that could allow quad cores into notebooks, but at the moment, the laptop would overheat or maybe even catch fire.
The other problem of today is that quad cores cost as much as an entire computer. In about 5 years the price will have probably gone down.
Also, as mentioned before, someone over at Apple would have to develop huge batteries to handle them. We're talking about six times more capacity to work for the same amount of time. Maybe in 10 years we could be ready to put quad cores in notebooks, but right now, it is implausible.
I'm not so sure it will be as far out as 10 years, but I agree that it will be many years before we see a quad-core notebook.
Power drain would be just unimaginable. Current battery power notebooks would be: Turn on notebook, open a program, battery drained. Of course this is probably being over-dramatic, but you understand the picture. The notebook would become a luggable desktop replacement that you would always have to have the power cord with you.
Heat would be another issue. I'm not even going to get into this. I remember people complaining MacBooks get to hot with current C2D chips. Could you imagine the complaints with a Q4 chip? Of course, I've had my Macbook since February 07 and can say that I've never had any overheat problems.
The MacBook is a solid machine imho. I suspect Apple will maybe bump up C2D speeds, maybe more memory, and bigger hard drives instead. I would love to see a graphics card improvement and so would my wife, but I won't hold my breath. I'll be buying her a MacBook soon, but we're going to wait a month and see what Apple does for two reasons. Please see this discussion for one reason on why we're waiting -
http://www.mac-forums.com/forums/showthread.php?t=61615. Second reason is because we can afford to wait. She's already been using my MacBook for her Photoshop and Illustrator programs.
It will nice to add another non-windows computer to our household. As of two weekends ago, only have 1 windows machine. That's our gaming computer.

Reformatted our old Dell computer we'd been using as a file server. Now is a file server running Suse 10 Linux. Works beautifully.