Why there are blocked websites anyway?
schools and work are the most places where you find blocked websites so if you want to access blocked websites at school and work you have to use a web proxy in order to access blocked websites
usually social networking like myspace, facebook, youtube blocked in these places
24p7.info is proxy you can use it to access websites at schools and work.
YSurfNow.info is another proxy you can use it.

some countries also block some websites for political or religion reasons and the only way you can access these websites is by using proxy.

Also proxies allows you to visit websites that have banned your IP.

have you ever wanted to visit website anonymously? proxies allow you to do this too because it hide you ip address so it keep your identity safe.

ofcourse proxies are not meant to be used to break the law or any other illegal activity.