Conclusion Notebooks are real PCs and in some cases even a real desktop replacement. But there are several major differences. Everything inside a notebook is tailored directly to that model. When you want to upgrade or change the VGA card or the motherboard of your desktop computer, you can get replacement products from different vendors that will fit into your desktop computer.
Notebooks have only very limited upgrade options.
MiniPCI, MDC as well as PC Cards are standardized and provide some flexibility. The battery makes the real difference from the desktop. Battery chemistry and capacity vary from model to model. Some notebooks support two battery packs, but this feature will add about 1 pound to the weight of the notebook. Mobile 3D graphics are one the rise, but about 1-2 years behind the performance of a desktop computer.