For those that didn't get in, keep trying. Next time you see a link, try again. I got in on my second try a couple years ago.
For those that DID get in. Make sure you do the household questions. You don't get paid, BUT from personal experience, I almost always get a REAL survey within a day or two of doing the household questions. I guess if they have something coming up they send the household questions to make sure you fit the requirements of the actual survey. So don't ignore those surveys just because you don't get paid for them. They're usually very short, just asking what sort of products you buy or have bought and they open doors to the paid surveys.
They always ask at the end if you'd be willing to try the product, but that's no guarantee - it's at the end of every survey. If I get in on the trial, I usually have the product within a few days.