Apple’s (AAPL) Siri, to paraphrase Alan Kay’s comment about the original Macintosh, is the first voice-activated artificial intelligent assistant good enough to criticize.

Good enough, in fact, that Asymco‘s Horace Dediu has suggested that voice-activation might be the next revolutionary user interface, as disruptive for future computing devices as the mouse, the scroll wheel and the touchscreen were before it. In his Critical Path podcast Wednesday (Back to the Future), he imagined a generation of mobile phones that run entirely on voice activation, without the need for expensive touchscreens.

So what happened Thursday is a kind of warning flag. From about 2 p.m. to 7:00 p.m. EDT, Siri suffered a nationwide outage. For roughly five hours, any question put to her by an iPhone 4S user in the U.S. was answered by a canned apology to the effect that the network connection to the servers where her intelligence resides was down.

And that’s one of the problems with Dediu’s vision of future computing. Not only is AI still in its infancy — a condition its been in for more than half a century — but it relies in its current incarnation on networks and servers whose unreliability you can bank on.

Good thing the iPhone still has a touchscreen.

Via VentureBeat, which first reported the outage and tweeted when it was over.