Personally, I use Twitter mostly to talk to people in the fields I work in, namely hacking and journalism. I don't see how either of those communities will move to App.net wholesale. If you want me to pay money just to have a conversation with you, I'm probably going to decide to just not have the conversation.
Ads on Facebook and Twitter don't bother me. I won't be paying to get rid of them. I don't even use AdBlock to get rid of them for free (partially because I think it's unethical to do).
My first post on Twitter was "trying to figure out WTF Twitter is". I subsequently didn't post for six months. I wouldn't judge the platform on what's posted in the first 30 days of existence. As for sustainability, $500k in revenue is more than Twitter had for years.
I don't know if it'll work, but I certainly hope it does.
I imagine it being pretty spam-free if it costs $50/year, as a bonus.
> You will be committing to pre-paying a full year of "member" tier service.