If you want to have some privacy, and you are fed up giving your email address, when you want to just register for a particular website - maybe for a white paper or software download, then you need to have a look at guerrillamail.com .
Visitors are issued with an email address that lasts just 15 minutes - which is more than enough time, to receive your password and log on details from whatever site you have registered with. And then, mission impossible style, the email address self destructs in 900 seconds (well, ok then it just disappears!!).
A fantastic way to stop the spam you know you will otherwise get.