Mid last week, Intel and Matsushita announced that they are working on an 8 hour notebook battery solution featuring Intel's low-power consumption technology powered by Matsushita's lithium-ion battery solutions.
Currently, (pardon the pun) laptops range anywhere from 3 - 6 hours, depending on what the users's power settings are. Users can try to extend battery life of a laptop computer by controlling hardware settings, such as how bright the display is, perhaps slowing down the CPU so that it uses less power, and powering down the hard drives so that they are not spinning needlessly. Others might remove their CD-ROM drive and replace it with a second battery. Battery life times are often given in ranges, because what software a person uses will directly affect how long the battery will last.
The operating system also affects how long a battery will survive over the long haul. If the OS insists on writing data here and there to the hard drive, or needs to run the drive to swap memory (virtual memory), the battery will drain all the more quickly.
Personally, to extend the battery life in my machines, I always turn down the display brightness, Open all of my applications once and leave them open, and try to use a RAM disk whenever possible to keep the drive off as long as I can. I also shut down any ethernet ports, and do not use my external mouse to save power.
I'd love to have an 8 hour battery though. Sounds wonderful!