I've applied to Fastclick twice, but never had a response. I'm thinking it's because I didn't give my SSN, which I have the valid right to keep as it is suppose to be for the government only. I was extremely hesitant about giving it to Google, but I trust them as a more reputable company (despite their faults).
But I was accepted by ValueClick. I think that AdSense accepts almost anyone, I've never heard anyone turned down by them, they must have money to blow.