The day I can code an iPad app on the iPad is the day I enter the post-pc era.
Or code, test & deploy web apps from an iPad.
Or design & layout web pages on an iPad.
We live in a post-mainframe era even though mainframes are still alive an kicking. But a mainframe isn't required create, test and deploy PC software. Once PCs are no longer required to create, test and deploy code for mobile devices we'll be in a post-PC era - that is, once PCs are no longer a required part of the general purpose computing ecosystem.