Which I encountered in an exceptionally useful book called Twitter, tips, tricks and tweets by Paul Fedries.
If you want to know more about the “why” of people’s use of Twitter and the ‘sweet spot’, you really should check out a fascinating article at the FastForward Blog called “The Science behind Twitter” by Robert Paterson.
And I’ve written a bit about it in the past. From January 2009, shortly after I got a twitter account, I wrote FaTheads: Facebook and Twitter, which stands up reasonably well, if I do say so myself.
More recently I did a short piece on work by Bob Selden Management Today) and Sherry Turkle (MIT guru) called Twitter lobotomises you?