Long battery life is the holy grail of all portable computer usage. Tablets tend to be better at it since they are designed for mobility and good battery life and usually at a cheaper price then the "ultra" mobile crowd. (Of course there are plenty of exceptions). The solution that I will use is multiple batteries that I just swap out. The thinkpad line has a recharger for the battery itself that can plug into the battery and recharge it without the computer (I am still waiting to get mine). Good discipline with multiple batteries is your best bet for long term mobility.

10 hour batteries are probably a stretch and are dependent on so many different factors that you could never know your actual limits. For example bluetooth wireless or ethernet wireless can certainly kill battery life along with bright screens and fast processors (or processors not optimized for battery life). The best advice would be to select a mobile processor from intel (AMD just sucks too much power), lots of memory to reduce hard drive access and integrated graphics are the focus of the hardware. You can get a solid state hard drive but those are pretty expensive for the benefit. From the user stand point dimming the screen and quick auto turning off the screen help a lot. Throttling the processor down (slowing it down) helps but extract too much of a performance hit, especially in Vista.

One good performance metric when looking at online reviews is can the portable play a DVD movie from start to finish. If not then the battery life is not very good.

During my training I worked at a clinic where they deployed an HP solution in which the computer batteries could be placed in a well that would store and recharge several batteries at a time. I am not sure if HP still makes this, you probably have to talk with an HP rep. This was a very effective solution for the multiple portable users, they always had a spare battery. You lost a minute switching out but that was not a big deal, just plug the unit in the AC and then switch the battery. I would certainly look into this if you are trying to keep multiple people mobile in a single location (like a clinic). Obviously the road warrior would just need a spare battery.

You can spend a lot of time and money looking for the ultimate battery solution but you will probably be disappointed. Just get a couple of spares and discipline yourself to keep then charged (which can be challenge to do, I know).