we're obviously past the age of posting toots via sms, so let's start with hashtags.
* aug 2007: hashtags proposed by users as irc-channel metaphor
* july 2009: twitter starts hyperlinking hashtags
* 2010: twitter starts tracking "trending topics"
but of course the mistakes that twitter did were to attempt to apply an algorithm to trends, meaning words and phrases could trend, and some hashtags could be filtered out or censored.
i think we're also past the point of external media hosting on twitpic/yfrog/etc, since internal media hosting has become far more widespread. so the next thing is to look at replying and boosting statuses. starting with replies, because boosting is a bit more involved in analysis.
* nov 2006: @ reply first used
* may 2007: @replies adopted by twitter
not much to say here. i guess i'd note that it makes a service more conversation than status-oriented, but that's about it? conversation is good
just about the last thing to add at this point is twitter's attempt to transition from a conversational platform to a curated content provider, especially since 2015. that's bad.
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