Regardless of whether you love it or hate it, Apple has pumped a lot of time, money and resources into the development and release of the Siri virtual assistant. And with rumors that the Siri API will be opened up to developers with the release of iOS 6, Siri is definitely here to stay. In my opinion, there is no reason why someone wouldn't want to have Siri installed on their device, after all, for those who choose to use it, the assistant can be extremely helpful in a lot of situations. And for those who don't wish to bother with it, it doesn't intrude in any way whatsoever.
