Hashtags on Facebook are an interesting new trend. It's particularly interesting to/for me, as a "Millenial"/Gen Y-er and someone who's worked for the past several years with mostly 18-21 year olds... because the resounding response I've heard has been along the lines of this --> :sick:
Hashtags, on Twitter, have served as a way to narrow down a HUGE ongoing conversation stream. i.e. On Twitter I follow friends, but also celebrities, writers, TV series, cultural topics, etc. So my stream is constantly overflowing with posts on anything from #poetry to #AskABlackMan to #TheWalkingDead. On Facebook, we already have a relatively "narrow" ongoing conversational stream: we're "friends" with people, so we can easily follow a single conversation. When I told my last class I taught at the local university that Facebook was getting hashtags soon, I remember one girl (quite humorously) loudly groaning and declaring she was "leaving Facebook for good." (She went so far as to pull out her phone to delete her account before I assured her she'd be back on the next day, ha-ha)
All that is to say ... I think if we're going to use hashtags on Facebook we need to know that some folks will like it ... a lot may not. It was assumed, for example, that the current generation would like it. But this generation has cultural "streams" of its own, like the hipster and counter-cultural divisions, or those who just don't like things to be "too much the same" (i.e. "I use hashtags on Twitter ... Why would I use hashtags on Facebook?" and "OMG, I wish Facebook would stop trying to be like EVERYTHING!" <--statements from my class) I personally use them sparingly, if at all. Maybe in a few years (or, lets face it, probably months) when it's become more the "norm" of Facebook I'll start using hashtags more liberally, but the way users can engage with them is even different between the two platforms. (i.e. on Twitter I can see any post by anyone who uses #poetry, but on Facebook privacy settings would keep me from that same level of engagement ... which has made some folks wonder if Facebook isn't just trying to "capitalize" on Twitter's success, or challenge Twitter's rising popularity by "mimicry.")