When Siri was first launched in 2011 there were a lot of unmet expectations. It didn't really seem to live up to its promise and most of the services shown in demos weren't available (in the UK at least). So for most iOS users it became a way of mucking around with hidden, automated responses. I've been asking around my friends in the past few months and nobody I know uses it on a regular basis.
By pure chance (ok I was mucking around asking Siri to marry me) and I found a useful feature in Siri. Then even more surprisingly I discovered another and yet another. Then I realised that whilst me and my friends had been mucking around ignoring any of Siri's uses, the team at Apple had been quietly improving the services underpinning it. Now it's really good.
It can relate food related questions to restaurant reviews, whilst using your location...
Simple OS functions such as iMessage, alarms, reminders and the calendar are also available with more straightforward questions
Most of these functions were a total surprise to me. Even though they've included some prompts to the functions behind the service.
My favourite feature is the connection to IMDB data.
This is becoming a really useful product