Hashtags didn't start out as a software feature on Twitter.
@chrismessina proposed their use, and for a long time, they were just a cultural norm.
It was months later that Twitter engineers turned them into links that went to a search result screen.
Same thing with @-addressing. It was a practice for blog comments that came over to Twitter, but there was a long time that there were no affordances in the UI to support them.
Same with retweets. People starting using "RT", and it took off.
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@evan @chrismessina Hashtags were links first in identi.ca, possibly also the "@" mention as well. I still remember Twitter getting that feature, and thinking, "finally."
