If you don't recognize the sender or the message title normally does not apply to you then don't open the email, send to Trash or mark & move to junk folder.
Also fyi since some simply do not know... there are Fake PayPal emails that are sent out every so often as well. At a former employer we once received one from "Wachovia" which had legitimate page links etc but the one page to request your new username and password was a sham.
The rest of you... no matter how enticing the email title sounds to you don't open it

.
Google:
Social Engineering and there's your answer to why it's done on a daily basis, currently it's a multi-million a year "industry" per say.
http://en.wikipedia.org/wiki/Social_...%28security%29