I've been sitting at this computer for quite a little while now with a tiny bit of success. How much time on average, do you spend taking these surveys?
After clearing my history and cookies, I start a session and attempt all of the daily surveys straight through to see if I qualify. That usually takes 20 minutes or so. If I've had no luck, I start a second session later in the day. As others have said, persistence is the key because the sponsors do vary the surveys. I qualified for one today:
GlobalTestMarket Survey - 05/11/2012 2012-05-11 $0.50 Approved
This was a BrainJuicer and only took about 12 minutes to complete. I count it a good day on FC if I qualify for one daily survey. Those count toward the $15 we need in offers to cash out and can be attempted once every 24 hrs. That's a good reason to keep at them.
Update:
After starting a second session, I qualified for a second daily survey today:
FC Daily Survey - 05/11/2012 2012-05-11 $0.70 Approved
This one was a long one and took about 30 minutes to complete. Just be sure not to rush through these. Some questions on this one were designed to eliminate survey takers who were not paying attention!