For anyone wanting to maintain some degree of privacy (but still enter competitions etc), it might be worth mentioning a free service called
SpamGourmet.com
Basic idea is that you register an account/username and then tell the service where to forward your e-mails. The service limits the number of messages that get forwarded to you (and the sender never knows if your e-mail address is with Yahoo! or Live.co.uk or GMail, etc).
You can provide a "whitelist" (domains or mail addresses that are 'always' allowed) but any messages from senders which have not be given this free pass, decrement a counter. When that counter reaches 0, no more unexpected mail comes through.
You create the mail addresses and the number to allow through (eg 5 to 20... 20 is the maximum even if you use a larger number). I tend to use a short name for the website and often add the year. Some examples:
mumsnet.2010.myname @ spamgourmet.com
asdastore.2013.myname @ spamgourmet.com
In both cases, only 20 messages would get through, but it's easy to add a permitted sender (eg [email protected] ) so the counter does not go down for those mail messages.
It's also possible to use other domain names run by spamgourmet... eg ... @ dfgh.net (short and fast to type, and no clue it is spamgourmet.com)
A few web sites cough when they see a mail address of text . number . text @ domain and may report some other error message, but typically it seems it's because they only expect to see firstname . lastname and get confused by 2 x "."
I use a different mail address for almost every website I use (and rarely do any of them have my 'real' GMail address), and if a site is ever hacked and mail addresses stolen, then after a small number of junk mails, anything more will be eaten by SpamGourmet and I don't know it was even sent out!