First, the obvious.
Twitterers in Iran have been sending us some pretty amazing stuff about what's going on there. This is the kind of unfiltered, real time, first-hand citizen reportage that is compelling in a way that traditional news sources rarely are. It was impossible before the internet.
Now the gripe.
The way some twitter maniacs are using this as a kind of justification for the idiotic goings on that represent 99% of the activity on Twitter is a joke. It's like equating my grocery list to a Hemingway novel because we both used a pencil.