Laptops today have "standby" mode, which disables everything the machine does except for keeping RAM alive. But the machine isn't really useful while it's in this mode. If you've stored a file on it, you can't get to it. If the file you saved is very large, uploading it to the "cloud" might take hours, and your favorite network filesystem probably didn't sync before you closed the cover.
You might have trouble backing up your hard drive (or uploading large files) at a time you're not using your computer for something else. Uploading big files is sort of a "non-foreground" task...you want backups to run while you're not using the laptop at all, not while you're streaming from Netflix.
Maybe to accomplish these things today, you have to leave your laptop plugged in with the cover open, glowing all night.
I copied 10GB of photos to my Windows laptop tonight, and then waited 40 minutes for it to copy over the network, with the cover open, sitting on a chair in the corner. The PC was across the room from my Mac laptop, which was downloading an OS update, with the cover open, also for an hour.
You would never design a device to work like that...it's like some mythological creature that can't be disturbed for fear that it will forget what files it was copying and make you start over. It's ridiculous, difficult, and fragile, but it hasn't changed in years.
Laptops wake up slowly compared to newer devices, and they can't do simple network tasks like making something light up when you get new email. When you're downloading a big OS update, and you leave the computer on, sitting on a table in the corner, it's not really using its CPU at all.
A much smaller CPU with very little RAM could do all these jobs well.
CPUs have gotten better at low power, even though they don't compete with the smartphone versions yet. So have hard drives, as they're being replaced by SSD. RAM still uses more than a watt per chip (smartphones have a lot less RAM than a laptop), and a WiFi radio uses <100mW.
One big culprit is the desktop-oriented chipsets, which use tons of wattage (like >10W) when you're not doing much with your PC. This is in contrast to the low-power chipsets that are emerging for Atom-based computers, which can stay in a true "idle" state for ten days. Presumably these improvements might come back to the PC, someday.
Intel has introduced a number of new idle states for their mobile platform that dramatically cut power during idle activity. This aggressive management of power state is why smartphones have long life, in addition to optimization of each component. Smartphones are good at waking up quickly, in response to a network event or a user-driven event.
But, I really just want a little smartphone in my laptop.
I want a computer that is a participant on my network, sharing files, backing up its filesystem, doing very slow uploads through my DSL, checking my email, all using a very tiny amount of power. Almost none of these operations is CPU-intensive, or even RAM-intensive. You could power down all but 64MB of RAM and I'd get by.
One complicated way is to make a hybrid version: a coprocessor that can access my disk and a portion of RAM when my "big" CPU is sleeping. Potentially a machine that runs most of its kernel on the low-power CPU, while apps run infrequently on the bigger one? For instance, an x86 CPU could wake up once a second to do a few cycles of work (a "sendfile" or an event-driven network stack?), handing off a buffer of data to a network controller and sleeping some more. If I'm doing a backup or uploading files, I could buffer a ton of data and go back to sleep.
In some ways, the PC model of "saving files" is very slowly being disrupted by the cloud. People are going to stop using Microsoft Office XP someday, in like 10 years. But the PC model is being disrupted much more rapidly by mobile platforms. Part of this is the square peg of PC hardware model that seems to have frozen some day back in the year 2000. The PC hasn't evolved to be part of the network, and in fact with the laptop, it's gone backwards, because you have to turn it off so much.
From what I can tell, people are not using laptops every day, and yet they are storing valuable data on them, and their home network connections can't sync everything instantly. This is just a very confusing state.
"Post-PC devices" have demonstrated some abilities to do background tasks all the time, not just when they're asked to. You could imagine tons of tasks that could run in the background.
The old platform might do well to try, just a bit, to keep up.