I don't claim this to be the right design choice, but it is worth noting that there are trade-offs to consider. Optimizing for "ease of asking new questions by new users" is probably not optimal.
It was incredibly confusing to me, a software guy, so I can't imagine how confusing it must be to the average user.
(This is with Ubuntu Lucid's stock FF3 on Linux, if it matters.)
As far as the existing "solution" of conflating search and adding a question, I give it an F. It has tripped me up before. I suggest going back to the drawing board.
It fails.
When I type a word that matches a topic and hit "enter", it sometimes goes to that topic, and sometimes it goes to the "add question" pop-up.
When I type a word that does not match a topic but matches the body of some answers, it usually goes to the "add question" pop-up when I hit enter.
I have not been able to discern how it decides which of these it is going to do.
While I was experimenting with it, it got stuck in a state where it always went to the "add question" pop-up. I could only search by clicking on one of the suggested search results.
If they intended this thing to discourage asking questions before searching, then someone goofed, and their testers are non-existant or incompetent.
The very last thing I want to do is sign up all my facebook friends and then ask a dumb question as my first action. The odds that I have a great question at the point of registration are pretty low.