Surveys are interesting because you can fill them out and then tag a friend (or several) to read your answers and also to fill out the same survey. They can then tag more friends and the survey will act much like a chain status update or chain mail. It can be a way to get to know a lot of friends in a short period of time. Surveys also have the potential to make your profile interesting. If friends know they can find a fun, interesting, revealing survey on your profile, they may make it a habit to visit often.
This article describes a variety of Facebook surveys that you can do - the random note survey, the how old survey and more are revealed within!