http://www.freedigitalmoney.com/en/Bitcoins seems to use the same ad interface. I did two surveys using bogus info during lunch just to see if it was legitimate (My time is more valuable than this, lol.) I received 0.11 bitcoins for one, and 0.14 for another within about 15 minutes for one and about an hour for another. I bet you it's the ad companies that cause this difference.