I had received an email from "Paypal Member Services" asking me to verify my Paypal account to my Yahoo! as well as Gmail account. Yahoo! mail did not give me any warning about the authenticity of the sender and I was about to click on the account verification link in the email as it looked very authentic. Good that I got an attack of paranoia and decided to directly go the Paypal website and check my account. When I received an similar email to my Gmail account much later, it flagged the message with a warning!
By the way, I have 50 Gmail invitations left. Just drop a request in the comments section if you need one!