Someone in the Q&A brought up a good example of a mashup implemented today in an undesirable method due to security reasons: Facebook accessing your GMail/MSN/... contacts to request more members. Contact sharing between applications is an excellent use-case for mashups, but I don't see it as a driving application. Certainly it gets to the heart of Crockford's talk: security is an excellent application for the Google Gears WorkerPools. If you are like me, you'll still be left thinking about how everyday web consumers will be motivated to download Gears, instead of walking down the questionable path of simply giving applications like Facebook access to all of your potentially private information.
Mashups are the most interesting innovation in software development in decades. Unfortunately, the browser's security model did not anticipate this development, so mashups are not safe if there is any confidential information in the page. Since virtually every page has at least some confidential information in it, this is a big problem. Google Gears may lead to the solution.Security is important and is critical to the growth of new mashup applications and I'll be happy if that alone brings us worker threads and off-line support, but I think the killer mashup is the one that makes all of this great data exposed through APIs and structured web pages and makes it accessible in new ways.
Mark, of diveintoaccessibility and diveintogreasemonkey fame, who I admire for his vision of accessibility wrote in his blog post "if wishes were iPhones":
I don’t understand this continuing obsession with buying things that you need to break before they do what you want.And with this thought I am reminded that the killer mashup/webos application is the one that takes all of those immensely useful web services out there and makes them measurably usable. And by usable, I mean giving the user control.