NVIDIA Optimus technology is a feature that allows discrete NVIDIA GPUs to interact with integrated graphics, either on a chipset or on a CPU package like Arrandale, in such a way that allows the performance of the discrete option to be available only when it is necessary and idle otherwise.  This ability allows notebook vendors to include a discrete graphics solution in their design without having to worry about have it sucking up power and bringing down battery life when not in use.  

We have tested a handful Optimus-enabled machines at PC Perspective and even if we haven’t always loved everything about the notebooks themselves, the graphics technology has continued to impress.  
Yesterday NVIDIA posted a new blog and video that demonstrates the updated Verde driver (that is what NVIDIA calls their own packaging of the graphics driver for mobile platforms) and some of the features it introduces.  One addition I liked was the ability to enabled a task bar icon that will let you know if the GPU is powered on or off more easily.  

Good stuff from the NVIDIA team as they continue to try to find a way to compete and innovate in the mobile space.  The only change I would personally like to see is some color changing or icon changes that will let me know if the GPU is enabled or powered down without having to mouse over the icon.  Also, an overlay that the user could enabled/disable while in full screen applications (like games) would also be a plus.