Every time I fill out my email address for a web site, I create a new address for that site. (Like ebay@wpidalamar.com for ebay). Since any mail going to wpidalamar.com comes to me, I get all my mail. Then when I start getting spam on that address, I know who gave it out, and I can simply block that incomming address.

Spammers have special programs that harvest email addresses from web pages. In fact, I get spam at the address ebay@wpidalamar.com, I suspect it was harvested from this page, and wasn't actually ebay selling my address to spammers. For that I have created a set of fake web pages that contain a lot of bogus email addresses. The thought being that this will fill their list with addresses that don't work, thereby limiting their ability to spam real people.