There are a ton of survey sites out there that pay you only in gift cards, so it's always nice to find one that offers PayPal cash payments instead. iSurvey World is one of these. It's a very new site, so there's not a lot of information out there on them but from what I can find, they're well liked so far.
Joining and taking surveys with iSurvey World is pretty standard. Just sign up, wait for your confirmation email to arrive, then head over to the site, navigate to your dashboard and answer some profile questions then start taking surveys. I should note that during the sign up process, you'll be presented with some offers to sign up for various things. You can completely ignore these if you want to. You'll be awarded $5 right off the bat as a signing bonus! Be sure to completely fill out your profile so that you can receive more survey opportunities because it's really important for them to be able to match you to qualifying surveys.
Every survey will add cash to your balance. From what I can find, the average 15-20 minute surveys award around $1-$2 with longer surveys offering higher rewards. You can cash out with $25 in earnings and it'll go to your PayPal account once it's done processing. It seems that it can take a while, 3-4 weeks at most, to have your earnings actually credit to your PayPal, but so long as you continue doing surveys and cashing out when you can, you should have a steady stream of extra cash.
Pros and Cons
I think one of the biggest drawbacks is the processing time, but if you put forth the effort and cash out whenever you can, you should see money rolling in pretty regularly. It's always great to find a survey site that will pay you through PayPal rather than with gift cards. I've also heard that people aren't disqualified from surveys very often here, so that's definitely a plus.