There is a recent and interesting post on MO: erdos-harary-tuttes-dimension-of-graph-progress-in-last-48-yrs that I know a friend of mine can answer. I had in mind to let him know via this feature:
Know someone who can answer? Share a link to this question via email, Google+, Twitter, or Facebook.
Then I realized that this box is not available for the questions that already have at least one answer. In other words, it seems that it is only available for the questions with no answer. Am I right? Of course, I can e-mail my friend independently. But, I cannot see the reason behind such distinction. Is there any reason? If not, I suggest to have that box for all questions.