An article in the Economic Times of India quotes Nielsen CEO John Burbank doubting the staying power of Twitter:
In the case of Twitter, [Burbank] says, "Especially when people like Ashton Kutcher and Oprah Winfrey came on board, there was a lot of hype. We looked at people who tried it, its repeat users, and found they were a little disappointed and didn’t come back. Twitter has created a terrific audience and a very important tool but we realise its not going to be the mass vehicle that a lot of people thought it would be.”
The article goes on to quote EVP Pete Blackshaw drawing the comparison to Second Life:
This approach has held Nielsen in good stead. The firm similarly had its doubts about Second Life. Says Pete Blackshaw, EVP – digital strategic services, NM Incite, Even at the time of the hype around Second Life there were early signs of doubt that this was not going to last.”
The difference between Twitter and Second Life is that Twitter has become infrastructure, and the messages sent via Twitter are spread much farther than Twitter itself, are heard and repeated by a wide variety of media, both vintage and vanguard.
It's not about how many people are adding to the conversation using Twitter, it's how many people are consuming and spreading that content. How many people create TV shows compared to those who view them? How many people use Wikipedia for reference compared to those who write and edit Wikipedia?
Second Life, on the other hand, is limited to people who are participating in realtime inside its projected virtual realm. Occasionally images or video escape its confines, but even then the audience is not widespread.
Twitter is a de facto standard database and timeline of the world's status data, open to all people and applications, searchable and persistent. It accumulates a record that trails the cursor of every passing moment.
If quoted correctly, Burbank and Blackshaw, don't seem to get it, confusing content creation with content consumption. Let them stay away; there will be plenty of people mining this opportunity in their absence.
[Update: Please see Pete Blackshaw's comment, below]