Several month's ago I noticed that one of my webmail clients, SmarterMail, had an option called "Plus Addressing." I didn't have time to look into it at the time, but then I was looking around last night to see if there was an option to create or include a vCard when I send out an email and I ran across this again and decided to take a look at the feature.
For those that do not know, plus addressing allows you to easily create throw away email addresses. Here's an example: firstname.lastname@example.org
You see, the portion of the email address between the plus symbol and the @ is ignored by the email server and delivers it to the real account. On some email clients, like SmarterMail, you can specify that the item after the plus should be treated like a folder and that items should be moved to said folder if it exists. So in the example above it would land email into the trash folder.