Facebook's application architecture (and indifferent attitude) means that it's all too easy to be sent dodgy links by well-meaning friends. Norton's Safe Web application for Facebook scans your news feed and wall, alerting you to material that could potentially cause a problem.
The free application uses the same reputation-checking technology that Norton uses in its paid-for products. You can set it to automatically scan new links, which is probably the simplest choice, but doing that also automatically publishes its results to your wall, so I ignored that option in favour of running a manual scan. Given Facebook's ongoing issues with security, it's still a useful tool to have in place for diagnostic purposes.