Of course it's enforceable. If you gain certain areas of knowledge working at a company where IP is restricted, then that restricted IP may be reflected in your

Of course it's enforceable. If you gain certain areas of knowledge working at a company where IP is restricted, then that restricted IP may be reflected in your personal code. This kind of practice is pretty common on a lesser scale, i.e. if you work on say a libc at work, then arguably you couldn't work on a libc or something very similar at home without risking a breach of IP. It just so happens that in Apple's case, they have fingers in such a large number of pies that it must take a great deal of work to verify that something /doesn't/ infringe on their IP.