Its success even at this early stage has been driven by its impressive speech recognition accuracy. Apple shows a demo of Siri in which you can ask it to split a dinner tip among multiple people (don't they know there's an app for that?) and Siri obliges, calling on the cloud-based computational might of Wolfram Alpha. It's the kind of task that Newton was supposed to help with, but anyone who remembers the initial state of its handwriting recognition would know that trying to write "What does each person owe for a 20 percent tip on a $205 dinner for a part of six?" would be enough to send you scavenging for the nearest napkin and pencil. Siri, of course, also has access to powerful sources of information that did not readily exist in Newton's day, such as location and commonplace wireless data.
Siri also impresses in its ability to follow a dialogue in some contexts. You can ask it what you have on today's agenda and then follow up with "What about tomorrow?" and it will show you tomorrow's appointments. You can then tell it, "Cancel the first appointment" and if it's a recurring appointment, it will ask if you want to cancel just that occurrence or the series.
But Siri has some unusual limitations. It can't open iPhone apps such as Safari or key websites such as Wikipedia by name (although it can initiate a Web search). It can dictate SMS or iMessage messages but not tweets despite iOS 5's Twitter integration. Siri can call up a preview of recent e-mails, but it is not (yet) Apple's answer to a way to have texts and emails read passively while driving, a task handled adeptly by apps such as DriveSafe.ly -- particularly on the BlackBerry platform.
Today, Siri ties into a relatively small subset of your personal information and calendar as well as Wolfram Alpha as a general knowledge storehouse and Yelp for restaurant reviews. But for this self-described "humble personal assistant" to realize what are clearly less-than-humble ambitions, it must tie into more cloud-based services. Unfortunately, the two at the top of the list are not at the top of Apple's buddy list these days; Google and certainly Facebook know much more about most Siri users than Siri does, although Apple can make up some ground with its own browsing knowledge furnished via Safari and its new partnership with Twitter. And while Evernote may not have Facebook's user base, chronology or unconscious knowledge population, it could add great value to Siri's knowledge of our life details.
While less important, there would also be advantages to having Siri integrate with more of the iPhone's own local content (although iCloud should bridge this somewhat), such as photos and videos. For example, Siri can't get the job done when you ask it to, "Email the last photo I took." Rather, it creates an email with the subject "The last photo I took" but no attachment. And if you tell it, "Take a photo in ten minutes," Siri shrugs that it is not much of a photographer (a self-deprecating concern that hasn't done much to stem the tide of many Facebook photos).
Siri is unique in Apple lore in that it is the first major UI paradigm not to be introduced with a fundamentally new device. Apple introduced its graphical user interface on the Lisa, its pen user interface on the Newton, and its multitouch user interface on the iPhone. (Even the modest scroll wheel debuted on the iPod.) Apple could keep it tied to its virtual desk as a limited assistant or make it a pillar for an ever-broadening set of features that could include information retrieval, life management, knowledge work, and proactive alerting and recommendation tasks. Siri itself, though, isn't giving anything away. When asked, "Why did Apple make you?," one of its responses is, "Apple doesn't tell me everything, you know."
Ross Rubin (@rossrubin) is executive director of industry analysis for consumer technology at market research and analysis firm The NPD Group. Views expressed in Switched On are his own.