The only issue with using "new mode of communication" to try to convince someone to use a service is that a new way of communicating appeals to people who are on the edge, but won't appeal to a widespread audience who might say "I don't need a new mode of communication, my current ones are working just fine."

It is a good point that twitter is revolutionizing gatherings of large groups of people (like at tradeshows and conferences) - maybe that is the way that it will get widespread adoption. Twittering at ballgames or concerts with lots of consumers? It's a possibility.