Some surveys are very iffy(if you see one worth 200 points or more, it's almost guaranteed you won't qualify automatically). As other reviewers have mentioned, it can be frustrating to spend time on a survey and reach 100%, only to end up not qualifying somehow for the survey. Also at the end of surveys sometimes is where the demographic questions are asked, which should come first in order to accept or exclude right away.
However, rarely have I had any issues with points not rewarding. And when that has happened, emailing customer service has almost always rewarded me with the right amount of points I was missing. Also redeeming rewards has been quite easy and I've had no issues in the year I've been on Swagbucks.
Overall, if you have some time to kill, it's a worthwhile site to try. Just be smart and not take surveys that aren't worth the reward. Ie: 40 points for a 30 minute survey.