Query Response Time
I often hear people say that inference based question answering systems will not be able to compete with current internet search engines because people are now used to less than a second query response time. That people will not be willing to wait one minute - even if the answer is better.
In a way I agree: With respect to traditional web search this may be a realistic hindrance to the introduction of more knowledge intense algorithms. But on the other hand, we can see that the internet will be accessed by devices other than the traditional desktop computer. Devices such as mobile phones, for which expectations on search have not yet formed. Just consider this prototype from Google
Searchers call a Google supplied number, where a prompt asks them to "Say Your Search Words." After a minute, the results are returned and, in the demo, the searcher clicks a link that leads to them. In a real-world application, the results would presumably be sent to a cell phone screen or in-car system.
Users do not yet have expectations on how long it will take to send them an SMS with a result after they spoken a query into their phone. They will not even realize that their car navigation system waited two minutes for the answer to the query for a personalized collection of podcasts with commentary about the area they are travelling through. They will still sleep while their eBook waits for the personalized newspaper (the eBook asked the alarm clock when it has to start).