I don't normally do so, but sometimes if a strange email address sends me an email (normally the types that say "Hello, I want to be your friend. Here is a picture of me etc."), I copy the email into Facebook to see if an actual profile comes up. It's not that I would report them or add them as a FB contact (of course not!) but mainly just out of curiosity. Is it a real person, or a spammer?
Also, one time I got an email from a strange address (I use hotmail, and the person had the email address like msnsupport@h..)that was saying that I needed to give my password for security checks. I didn't believe it really (i'm a bit paranoid on the internet) but I checked the email address on Facebook, and turns out that the person was stupid enough to have his actual profile attached to the phishing one! Needless to say, I blocked both.
Otherwise, I don't use facebook for things like that.