depends...
If you are marketing to business people, it seems to be best to puff yourself up as much as possible. they eat that shit up, as far as I can tell. I bet his massive ego gets him some work.
When marketing to technical people, the opposite seems to be the case. In my experience, it's best to say "Oh, I'm nothing" and then proceed to show or do something pretty cool. Adding in a few words like 'perhaps' or "I believe" can make your message come across much more positively when dealing with the technically focused, and can do the opposite when dealing with the business focused.
(note, while "I think" or "some people believe" adds a touch of humility, "In my experience" can go either way. It can imply that you feel you have a great deal more experience in this area than the other people in the room, adding to confidence/arrogance, but it can also imply that what works for you might not work for others, making you seem less confrontational.)
This is one of the things I find interesting about hacker news; it seems to be populated by people who are halfway between those two worldviews.