Personally, I've noticed that it's great for initial discovery.

For example, if you know nothing about a topic, it can give excellent pointers and summaries of whatever you want, in just seconds.

Sometimes it's useful to ask some questions you would ask a friend, but there's no one around at the time. Silly example would be: "what should I absolutely bring to X", in case you don't want to miss anything and you need to leave right now.

The possibilities are endless really, it's an exciting technology, and it makes Internet search a bit old fashioned.