Not sure when it happened (my best bet is that it came along with Gmail v2.0), but Gmail’s filtering system now (finally!) allows you to automatically mark as read, something I’ve been clamoring for since jump.
I get various e-mails that I never really need to see, and before this recent addition, I couldn’t automatically mark them as read, which meant I needed to manually perform some action on them even though I didn’t care at all about their actual content.
For example, I get a weekly e-mail from WordPress containing a complete backup of my posts (using the WordPress Database Backup plugin); I take it on faith that the plugin is doing its job each week and so I don’t need to see these e-mails. The same goes for student loan payment confirmations, which, until now, required me to constantly go to their label/folder and manually mark them as read.
You can understand how this inefficiency could drive me up a wall (OK, maybe you can’t understand that, but no matter!). Now I can receive, skip inbox, apply label, and mark as read, all without ever having to see or even know about the e-mail.