1 - Be very careful where you publish your address
Publishing your email address anywhere online can invite much unwanted email (or "spam"). There are companies and individuals who gather email addresses from a variety of sources such as websites and newsgroups, or simply buy them from other businesses. These lists can then be used for mass mailing or even sold on to other parties.
2 - Do not respond to spam
The majority (if not all) of spam is a complete waste of your time. When you respond to spam you will have confirmed that your address works and it will be used and passed on to many other people who will bombard you with more of the same.
3 - Set up another email profile for 'at-risk' activities
If you frequently use newsgroups or feel you must display your email address on your homepage, it is a good idea to have two different accounts - one for your personal email that you give only to trusted people, and the other for giving to less reliable sources or for publishing.
4 - Be careful who you give your address to
Many websites claim to 'need' your email address for a variety of reasons and indeed this may be the case for some of them, but there are many that will only use your address for third-party activities - that is to say, they will use it to send spam and/or sell your information on to other companies.
If the website genuinely needs your address then they should have some form of Privacy Statement detailing exactly what your information will be used for. If not then it is probably better that you do not give them any information at all.