This question is surprisingly common. The headhunter or HR person asks “Rate yourself on a scale of 1 to 10.” For example, “How strong are you in C#, on a scale of 1 to 10?”
Whenever someone asks that question, I mentally translate it to the interviewer saying “I’m a clueless twit who knows nothing about hiring programmers.”
What am I supposed to say? If I say “10″, I sound overconfident. If I give a number too low, they’ll filter me out for giving a low answer. I usually say 8 or 9. The correct answer is “I’m highly skilled. I’ll be one of the top performers in any language quickly, even if I’ve never used it before.”, but that response is too complex for someone dumb enough to ask that question.
That question is “useful”, because it tells me that the asker is completely clueless. That’s the most frustrating part of searching for a job. Most of the middlemen are technically illiterate. They can’t do any evaluation more complicated than matching keywords on a resume.
That question completely misses the point. If an interviewer asks you to rate yourself, obviously you’re going to give yourself the best rating possible. The interviewer has to be technically oriented himself, so he can tell the difference between competent people and fakers.