I personally haven't bothered but I know a lot of my alliance m8s have done the survey thing with good results. The have about a 10% success ratio on whether or not the are eligible.
I've tried 8 now (as the little pop up box in-game says...it keeps count of attemped and completed) and I haven't run into an eligibility problem yet. What I keep running into are surveys where the requirement is "to create a free account with legit info" or to "fill out this survey". These things I get done. However, I must then pile through 90 pages of offers (many of which repeat over and over again) and I can't get a free iPhone 3GS unless I complete 2 offers.
Yeah, I make the account and am awarded no credits then they try to lure me into getting a free iPhone. Too bad I despise AT&T, and iPhones, and scammers, and completing dubious online offers. Otherwise they'd totally have me hooked.