HN user
Don't really care about the startuppy angle, but I like the idea of SMS as fruitful constraint. The idea of building an app that delivers its full experience to SMS, browser, or something wearable like Glass is pretty sexy.
Which is going to be a huge limit on sustained value/adoption, for better or worse. Bitcoin's rooted in the community most capable of stealing it.
Worthwhile (and complicating) read: http://www.snopes.com/politics/business/mpa.asp
Another take, maybe more slanted: http://www.addictinginfo.org/2013/03/28/conservatives-laugh-...
Anecdotally, most folks I know use Reader every day at both home and office, but "use" G+ only to the extent that it's plugged into other Google services.
Tried this a few weeks ago - as a relative beginner, thought it was a fantastic introduction. (Pretty effective promotion for Code School, too.)