Playing with Twitter reminds me of blogging circa 2000. Back then, all weblogs were personal in nature and most people used them to communicate with their friends and family. If I wanted to know what my friends were up to back then, I read their blogs. Now I follow Twitter (and Flickr and Vox).
The reaction to Twitter mirrors the initial reaction to weblogs...the same tired "this is going to ruin the web" and "who cares what you ate for dinner" arguments.
Also like blogs, everyone has their own unique definition of what Twitter is (stripped down blogs, public IM, Dodgeball++, etc.), and to some extent, everyone is correct. Maybe that's when you know how you've got a winner: when people use it like mad but can't fully explain the appeal of it to others. See also: weblogs, Flickr.