The core differences of integrated graphics processors (IGPs) vs dedicated video cards (GPUs) are :
- IGPs uses significantly less power and generate less heat than GPUs
- IGPs uses/shares main system memory whereas GPUs have dedicated memory
- IGPs are performs significantly lower compared to GPUs (especially Intel IGP solutions)
- On a desktop, if an IGP breaks down, you can't replace it short of replacing the whole motherboard. However, if a GPU break down, you can replace just the GPU alone.
So when you should consider one or the other? I'll try to make your decision simple.
- Games/Performance > If your priority is in playing 3D games or high-performance computing, get a dedicated GPU.
- Battery Life/Heat > If you are more concerned about having a notebook that can stay away from the mains, and won't fry your lap with heat, get an IGP.
- Desktop/Notebook > If you are on a desktop, get a GPU (even a cheap one, such as the Nvidia 9400 or the ATI 4350). If you are looking to purchase a notebook, consider the above 2 points.
Personally, I predominantly game on consoles and my iPhone nowadays. If you are going to get a notebook, try to see if you can get one with the Nvidia 9400M chipset (IGP, but damn fine performance for an IGP solution). However, I do have a souped-up desktop rig for gaming, which is currently turned off 90% of the time... till Diablo 3 gets released. :)