AnandTech has compared the switchable graphics technology from AMD and NVIDIA by pitting Dynamic Switchable Graphics vs Optimus, you can read it over here. The reviewer concludes AMD's dynamic switching is fine when it works, but complains that out of sixteen games, not even counting OpenGL titles, four of the games didn't work properly with dynamic switching. NVIDIA's Optimus on the other hand worked fine with every single game without any tweaking necessary.
Before we get to the actual meat of this review, we have a disclaimer to make: both laptops we’re comparing came to us via NVIDIA. Now, before anyone cries “foul!”, let me explain. First, we asked AMD for just such a laptop back in May, and they haven’t been able to get us one yet (though it’s likely as much the fault of OEMs as AMD). We also only just received our first Sony laptop (from Sony) in a long while, and we received the VAIO C from NVIDIA first. Finally, the laptops came boxed up, unopened, with all the standard fluff you’d expect from retail notebooks.