Although there are appreciable comments and an answer after this question (thank to Robert and Acattle), I am much seeking for a Knowledge branch, (e.g. an "NLP sub-task") than an individual research:
I'm searching for an "NLP subtask" which can help recognizing if a micro-blog post is asking a question and more generally "is answerable" or not. For example the tweet
"A problem shared is a problem halved - so tell us about your one weird phobia"
is not a question but is answerable; or the tweet
"xxx Town is on fire"
is neither a question nor answerable; the tweet
"For our next area spotlight: what's your favorite thing in xxx Garden, and why?"
is a question seeking for answers; but the tweet
"What do you do in your Time Out? xxx and @xxx want to see your x minute films about your London httpx://xxxxx"
though is a question, not seeking for answers.
This recognition, itself, can be of my interest.