This story is suggested by Indonesian Twitter user, @budip, Budip Putra.

When bombing first rocked Jakarta on July 16th 2009, Indonesian twitter users not only helped break the news to the world, they also found a metaphor for unity and strength in the hashtag they picked for their tweets about the incident

Budip described how Indonesian Tweeples consulted one another about the choice of hashtags.  Instead of the more descriptive "Jakarta Bombing" or "Indonesia Bombing", Ismet @ifahmi coined the hashtag #IndonesiaUnite.  His suggestion was immediately adopted and #IndonesiaUnite quickly became the rallying cry for an entire nation on Twitter.  At one point, #IndonesiaUnite became one of the top ten trending topics. 

This is a perfect story of the good use of a hashtag, as a symbol of hope and unity rather than a mere description of tragedy and despair.