Nicholas Carlson of Alley Insider writes The Case Against Twitter, By The Numbers, a good paradox piece which points out the difficulties Twitter has in retaining mainstream users.  

Carson points out he is pro-Twitter personally, and then raises questions on the abandonment stats:

• 10% - The percentage of users that account for 90% of all Twitter messages, according to the Harvard Business Review.
• 60% - The percentage of Twitter users that quit the site after a month, according to Nielsen estimates. The stat may be skewed by people who use Twitter via SMS or desktop clients like TweetDeck.
• 74 - The number of days the average Twitter user goes between sending a Twitter message, according to the Harvard Business Review.
• 6 - The number of days since Oprah last updated her Twitter account.
• 270,000 - The difference between 5.60 million, the number of unique visitors to Twitter in the week after Oprah signed up for the service, and 5.33 million, the number of unique visitors to Twitter the next week, according to ComScore.
• 100 - Things more popular than Twitter as of mid-March, including Kenny G’s album Breathless and the forgotten Batman spin-off Catwoman.
• 51% - The percentage of people with Twitter accounts don’t use the service at all even once a month, according to All Things D.
• 19% - The number of Twitter account-holders who use the service once a day or more, according to All Things D.

Interesting stats, but I’d still bet on Twitter. 

None of the infrastructure of commerce around Twitter is built.  Real-time search will be a huge business.  Today, it’s just a tiny link in the footer. In certain markets, Twitter works very well - blogs and breaking news. 

60% - most tweets I see are through a client, so this number is meaningless. Last I looked Twitter’s traffic was growing like crazy.  The rush of new users in the past couple of months have been celebrity-generated and/or domain squatters. It would have been more shocking if new Oprah-hatched users had taken wholeheartedly to Twitter at this stage of it’s development.

Traffic equals money, generally speaking, but full monetization of traffic takes awhile. FB isn’t at its revenue max given it’s traffic, they are just figuring it out. Google was around for years before they IPO’d, Adwords/Adsense weren’t built in a day, a whole new industry needed to crop up with contextual advertising metrics, etc. Companies that will be fueled by Twitter ads barely exist at this point. 

For a good counter-argument about what’s coming up for Twitter and mainstream adoption likelihood, the Steven Johnson Time.com How Twitter Will Change The Way We Live piece is terrific.