Great article. As an attendee I really love it when a conference starts and ends with a keynote just like you described. Inspiring, not to specific and fun. At the start of conference it is fun to set the tone and wake you up if it is early. When the conference has multiple tracks I love it when the last talk of the conference is the same for everybody, just to end together. That talk should send you home with the energy to start doing something. Again not to specific about something so you just reflect that on what you are doing instead of what somebody else is doing.

As a conference organiser these thoughts help me make decisions on who I invite to speak at the beginning and at the end of our conference. Maybe not only who, but definitely the content of the talk. We ask our keynote speakers to make it fun, inspiring and so far that always worked out for us and our attendees.

As somebody who would like to start speaking at conference your ideas and links really boosted that idea. Not that I want to start do keynotes, but I think those rules and the link to the questions Kent Beck sums up.

By the way, really loved your talk at Nordic Ruby!