I’m catching up with Gmail blog posts and thought [this tip](http://gmailblog.blogspot.com/2008/03/2-hidden-ways-to-get-more-from-your.html) was particularly useful. You can modify your Gmail address when you give it out to different organisations, so the next time you get emailed (or spammed) you know who the source is.
You can add a ‘+’ or ‘.’ after your Gmail username and emails will still be delivered to your main account. The benefit is that you can filter these modified email addresses. I’m going to start doing it now when I sign up for new accounts and newsletters.