March 3rd, 2008 | Published in Gmail (Google Mail)
A few months ago I wrote about how using colored labels with filters can provide an entirely new way to visualize your inbox. I just started using a feature that further helps me quickly prioritize my email. When enabled, "personal level indicators" put arrows next to messages in your inbox so you can tell if an email was addressed to you, a group, or a mailing list that you're on.
A single arrow ("›") is automatically placed next to emails sent to you and others, and double arrows ("»") next to emails that are sent just to you.
I personally get a ton of email from lists (mostly from my college days when I subscribed to student group lists after a campus activity fair), so it's helpful to see my inbox annotated with arrows that tell me which emails are likely to warrant replies. If I get a bunch of emails with no arrows at all, I know they are probably from mailing lists. Give it a try for yourself by switching the "Personal level indicators" option to "Show indicators" under Settings.