The signature feature on the iPhone 4S that Apple (AAPL) unveiled Tuesday is Siri, a so-called intelligent assistant that depends on a lot of fiendishly complex artificial intelligence systems — voice recognition, understanding context and natural language — working flawlessly a high percentage of the time.

Few companies know better than Apple the risks of counting on applied AI to sell consumer electronics. Apple’s Newton Message Pad never quite recovered from the drubbing it took in the popular press — especially the Doonesbury strip posted above — because its handwriting recognition software failed more often than it worked.

The Newton, which was released in 1993, was a pet project of John Sculley. Steve Jobs killed it in 1998, shortly after he came back to Apple. We assume he wouldn’t have signed off on Siri if he didn’t think it was ready for prime time.

But we’ll find out soon enough.