The last few years I have kept my eye on various scams. It all started with phony invoices for bogus directories. Then came the massive surge of "Nigerian Scheme" e-mail messages arriving in our e-mail boxes. As of late I've been receiving messages supposedly from e-Bay and PayPal saying there is a problem with my account, encouraging me to sign on and update that account. The problem is, I don't have accounts with these services. But suppose I had? The U.S. Dept. of Justice has now released a report on fake websites used to gather information--this scam is called "phishing". See: Special Report on "Phishing".
I often check this website to determine if something is a hoax: Current Netlore - Internet hoaxes, email rumors, urban legends and also RCMP Frauds and Scams. See especially the RCMP's list of scam files at the bottom of the page.
When in doubt, I usually ignore and delete e-mail, faxes, and invoices I don't recognize.