Since each of those cores is supposed to have twice the graphics processing power of the current SGX535 in the iPhone 4, iPad and the iPhone 3GS, we are looking at roughly 4x bump in the graphics and video performance, compared to those oldies. Good, now we can sleep better, knowing that the iPad 2, and, most likely, the iPhone 5, will encode and decode full HD video with ease, which should be a pleasure to watch with the iPad's new screen resolution. They'd better ship with at least 64GB of storage then.
PowerVR is a part of Imagination Technologies, which licenses mobile graphic chipset designs to companies who actually produce them, like Samsung, similar to what ARM does with its mobile CPU designs. In 2008 Apple, Samsung and Imagination Technologies started their cross-licensing partnership, which resulted into what went into the iPhone 3GS, iPhone 4 and iPad for Apple, as well as Samsung Galaxy S and Samsung Wave for Sammy.
The notable difference between the two companies is that since Samsung released its handsets later than the 3GS, it used PowerVR SGX540 in its 1GHz Hummingbird chipset, which pushes about three times more polygons per second than the SGX535 we have in the iPhone 3GS. The theoretical 90 million count makes Samsung's Hummingbird chipset still the undisputed leader in graphics, beating even NVIDIA's dual-core Tegra 2.
PowerVR SGX543, in its quad-core configuration, is supposed to go into Sony's PSP2, so that's a vivid testimony of its abilities. Still, Samsung will be using ARM's own graphics subsystem called Mali in its upcoming Orion chipset, which Sammy claims pushes 5 times more of those little triangular thingies per second than the previous model. Depending on whether that means the previous Mali models, or the Hummingbird chipset, Orion is rumored to process anything between 130 million to 450 million triangles, so the next-gen iPad and iPhone will be given a good run for their money, all for our geeky benefit. Don't you just love competition?