I didn't know David as well as Rich Tehrani or Fred Knight, both of whom have written wonderful eulogies to him over the weekend, but what I can say is he was a gentleman and as industry analysts went, David was one of those who knew his stuff and didn't shout about it. He just did it right, all the time.
I started running into David at VON and IT Expo events many years ago. He always had a kind word, a smile and would reach out to me to talk about things. He also always took time to have briefings with my long list of clients.
David did his thing without a lot of flash. But he was a nice person through and through. Like with the passing some years back of Russell Shaw the VoIP and IP communications community has seen another one of the really good guys go before their time.