The Tumblr “ask” function does not appear at a post. The function appears at the icons on your dashboard!!! It’s really quite nifty! I’ll let Charles (of CountryBoyLife) explain:

As far as I know there isn’t a limit, or at least I haven’t hit it yet, as to it’s advantages over formspring.me, it is as yet a case of swing and roundabouts, since formspring.me is cross platform so you can embed the same code in say SU and Tumblr. Tumblr’s version has the advantage of being accessible from the dashboard via the Tumblr’s avatar, hover over and click the ( i ) and ask comes up - it’s also probably easier for someone with no experience of basic html code to enable. As I remember from reading the announcement ( I may be remembering wrongly ) a more complete messaging service might be coming, as yet if you answer a question using Tumblr’s Ask Me form you get the joy of using Tumblr’s visual editor, but, your reply becomes public ie posted with question to your blog. The work around is to go the asking User’s ‘ask me’ and reply by ‘asking’ them a ‘question’.

And yes, FrenchTwist, all questions and answers are private. Both questions and answers will appear at the “messages” link in your dashboard.

I have to take back everything that I said about the new Tumblr “ask” feature. Now that I know how it works, I think it’s cool! :-)