Apple claims the A4 is great for battery life and early reports based on hands-on time with the iPad say it's pretty fast. Indeed, Apple seems to be off to a good start with its in-house chip development. But the A4 is not all that different from what Nvidia and Qualcomm are putting out for other tablets and smartphones. According to Bright Side of News, it consists of ARM Cortex-A9 MPCore processor clocked at 1GHz (the same found in Tegra and the Snapdragon), an ARM Mali 50-series graphics chip, and a memory controller.
What this means is that the chip is predominately ARM IP, branded with the Apple name, and that other manufacturers will have very similar hardware options to choose from when they design their own tablets -- or they might as well opt for an x86 part and a full-fledged Windows operating system.