Wow, there's been a lot thrown out here in this thread. Ok, first, most survey sites have a "discontinue" or "drop me" option that you can choose.
On FC, though, I think the answer you are looking for is this:
The survey sites that are offered on the "offers" page are sign-ups and, of course, no you can't sign up for what you are already signed up for. However, the survey sites that are on the "daily" offers page are just survey attempts that you can try daily regardless of membership there or not.
I am a member of about forty survey sites and I get credit here very often as well as from the webpages themselves.
I agree with the poster above who said that signing up with a lot of sites can be frustrating because many, many days I have over 200 e-mails in my inbox and can only do what I can do. But it is so rewarding to find checks from three sites in my mailbox in one day, plus a gift card payout and freebie gifts from sites, etc.
But even being a member of something like forty sites, guess who I think is the easiest work, the quickest crediting and the most common cash out? FC is the one with the easiest to reach goal with the easiest offers to get there.
Hope my little 2 cents was of some assistance. Welcome and Good Luck to ya!