I don't know where you are located, but iAds went live in the US and the UK on July 1st.
So you can't really call it early impressions 4 months later, unless you don't live in the US or UK, then you can. As to your question, eh, I have only ever clicked on 1 iAd, and that was back on July 1st as a trial (I normally ignore ads of any kind)