Crosmando: You know what would be a great idea? A "laptop" which looks like a laptop, as in has the monitor, keyboard and ports for peripheries, but doesn't have any hardware in it, and you could just plug a (long) HDMI cable in the back of it from your main desktop computer's GPU.
That way you could have the benefits of a desktop computer (more power, compatibility, not running out of charge, etc) combined with the benefits of a laptop (being able to sit back on your bed and play games).
It's an interesting idea - what you propose would simply be a gaming-specific iteration of the old
Network Computer or
Thin Client idea, except that the server would be in your own house. This would actually be a perfect application for [url=http://en.wikipedia.org/wiki/Thunderbolt_(interface)]Thunderbolt[/url]. Have one cable provide everything - display, data, even power. The problem of course is that outside of that one niche case it'd be practically useless for anything else. I think what we'd really want in the end is a computer that would essentially go back to the old idea of the Network Computer - for gaming, that would essentially be OnLive (though for it to truly shine, we'd need something like widespread WiMax/FiOS adoption). As a matter of fact, I'd be willing to bet that Razer likely has one of their pie-in-the-sky prototypes doing exactly what you say in one of their labs right now.
"They went ape over the Switchblade, and went crazy for Project Fiona...they're going to love this! Yeah! We're going to save PC gaming!" :P
Crosmando: As I was saying, the "mobility" of laptops is a joke anyway, a few hours even doing low-power intensive things and the charge is gone, from the people I've seen using laptops, they always seem to be using it plugged in anyway.
I think that's because most people have budget laptops with less-than-optimal power management functionality, and have cheaply designed batteries. I'd bet that if you get into the territory of business class laptops you'd do much better in terms of power consumption. And that would go even further if you went entirely with SSD/Flash storage and got rid of other mechanical components like an optical drive.
I do think this is one area where Apple has had the right idea in terms of notebook design - by integrating the battery into the notebook's case you can get rid of all of the various internal structure needed to support a removable battery and just pack the internal structure with as many battery cells as you can. The optimal situation though would be to still make the battery itself easily accessible (as it was on the old aluminum unibody MacBooks).